Different types of FTL in the same universe.

I think the general assumption in scifi settings is that there is A Way to get ftl travel and therefore people, even if they tech to it differently, arrive at the same result. It would be extremely complex to detail the different methods, but I suspect one overall better method would eventually emerge.

My favorite FTL is the one in Hyperion which kills people who travel in such ships--turns the crew into paste. They just use resurrection technology when they get to the other side.

The Liaden universe has at least two distinctly different methods of FTL.

Also even Star Trek shows "warp" speed being achieved by different technologies: standard warp, borg conduits, and whatever the Q do etc.

I actually do find this notion to be a very "interesting mess." In some ways, it complicates things if people are using different technologies, but in another way, this opens up all kinds of neat problems to think about and overcome. If you've got some people actually using some kind of linear movement like warp drive, versus another culture who's entire technology is based on folding space, for instantaneous travel, a la the Guild Navigators in Dune, this instantly creates some interesting issues. And then there's the question of sharing technology, since, if other races find an FTL technology that seems to work better than their own, they might be interested in adapting that technology. Or, more interestingly, another culture sees a different technology that appears to work not as well as their own, but realizes with some improvements, that "inferior tech" could vastly improve and overtake their current technology. Lots of fun ways to go with this, especially once military conflict enters the picture.

You could also have different species eschewing particular forms of ftl for moral or philosophical reasons. For instance, a species that believes in souls might think that a form of ftl similar to Star Trek transporters is actually killing the individual and creating a duplicate at the destination. A species with a strong moral character might have a problem with an Alcubierre style drive spraying lethal levels of radiation in front of itself. (Has anyone ever considered that might be the explanation for gamma-ray bursts?)

Neverness by David Zindell was as all-around crazy-ass Dune clone (which I highly recommend), and featured one of my favorite FTL ideas. Pilots are a trained caste of mathematicians that traverse a multidimensional mathspace, solving equations as they go to make the journey. it's pure goobledegook, but very exciting, and has the advantages of both taking a non-trivial amount of time and giving pilot something to do.

I always had the vague idea to do something similar, where FTL is possible because of some alien superhighway imprinted into the Bulk. But, meh, FTL kind of annoys me.

I'd imagine multiple forms of FTL would roughly sort themselves into layers, more sophisticated and faster (but weirder and more dangerous) forms of FTL would be based on the same principles as the cheaper and more pedestrian varieties, though different approaches could seem totally alien and wrong to each other. I guess I would try to unite the types of FTL I use around whatever big lie I tell to make the technology possible, or at least try to handwave that scientists are working on a United Theory of Alien Stardrives.

Dennis E. Taylor said:

For instance, a species that believes in souls might think that a form of ftl similar to Star Trek transporters is actually killing the individual and creating a duplicate at the destination.

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That's exactly what they do do. As evidenced by the TNG episode Second Chances.

I teleported home one night with Ron and Sid and Meg
Ron stole Meggie's heart away, and I got Sidney's leg -- Douglas Adams

i'm a Stellaris fan as well, but I only play Warp. To hell with the other FTL modes. I'm too obsessive-compulsive to play with wormholes (gotta survey every star in range before building more!) and I'm sick of having some overpowered space amoeba blocking my only hyperspace route out of a cluster.

In my universe, your choice is between quick-and-dirty DIY wormholes that have the unfortunate habit of spontaneously exploding and irradiating entire systems, or the bespoke hand-wavy drive that my alien overlords will happily license to you, at the cost of your soul. Choices.

Makes sense to me. Consider the different tech used in aircraft. Ones with jet vs reciprocating engines, wings vs revolving blades, and so on. Different flight regimes require different hulls: near ground, stratosphere, space.

I'd expect how advanced the civilization is to effect the kind of propulsion. Such as one a hundred years beyond us, to a thousand years, to a million years.

I've been jamming on the idea that if you've got two forms of FTL, regardless of the order which you develop them, that you'd want the "better" one for yourself and the "lesser" one is what you'd sell to folks, so as to not have them come back to haunt you.

Also, different forms of FTL would lead to interesting combat strategy differences.

In some stories I'm writing [and still shoring up for agent querying later on], I settled on two types of FTL. I wanted it to be as reality based as possible, in regards to what is physically possible for technology, and FTL techs I picked are actually the only 'rule breaking' techs I have. Everything else, such as spacecraft centrifuges, magnetically confined plasma windows and suspensions for hover vehicles, fusion, antimatter and biotech and nanotech, is all plausible.
But the FTL methods I selected are all theoretically possible. First is the good old Alcubierre drive, which requires exotic matter with negative mass to be collected, and a lot of energy, though less with better calculations and a warp bubble shape that's also being oscillated it seems. As is theorised in real physics, the ships that use them in my story have collected particles on the outside of the bubble that fly forwards when they drop out of FTL, so they have to be careful not to be pointing at whatever they're headed for, and it gets more powerful the further a ship has traveled in one single jump period. In world, this is a war-crime if its intentionally used in combat among the associated races and governments.
Second is not used for travel, not by my Tier 2 civilizations anyway. Microscopic wormholes are formed, and held open by tetrahedrons of exotic matter with negative mass in the middle of their throats. The tetrahedrons have gaps inside them, which is what restricts how big an object that traverses the wormhole can be. In my stories' case, they use them as beamed communication shortcuts, effectively enabling near live communications so long as you are close enough to a wormhole satellite, and it isn't too far from the chained ones and your recipient. Its basically a hyperadvanced telephone exchange of sorts, a spacetime bent fibre optic cable. Of course, I leave the door open for more powerful cultures they might find to use bigger wormholes, big enough to traverse, or big enough to fire weapons through, or even just big enough to act as interstellar peeping hole type periscopes from light years away.
The one white lie of physics I implement is the exotic matter, which is theorised as some form of concentrated dark energy or alike in actual physics, to generate the negative mass conditions to expand space and hold open a wormhole. So exotic matter is a valuable commodity, though one that has to be manufactured, as it doesn't naturally occur.