So, as a professional book designer, perfectly blunt: none of the covers you've shown here look professional and I have a hard time believing that any of them have had the input of a genuinely professional graphic designer. They look remarkably like most of the covers I have seen on this forum: homemade, without polish, and without any kind of care given to typography. While it is true that a designer that does not have a grounding in book design might struggle to develop a cover, any designer worth their salt will have a grounding in typography.
The most common mistake that people make when developing their covers is (apart from not budgeting for a genuine designer) affording undue importance to the imagery and forgetting the type. Then they go online and hear talk of "negative space" and make everything flippin' tiny. Julianne is so right, you're going to have to sell this in thumbnail first, before anyone sees the cover fully. That doesn't mean making everything huge, it just means keeping things simple. The best covers aren't the most elaborate with the most beautiful type, they are the ones that a fit for purpose. I always tell people to look at other covers, not in your genre - as you're more than likely to get Google screens full of similarly homemade covers or likely to follow useless trends - but at the great covers. Go to publisher's sites and find the artists they use, look at David Pearson and Jo Walker for some specific examples. Look at enough and you might be able to pick up patterns in how they present their covers. But remember: the content, not the picture, is the most important.
My advice to people is always to budget carefully and find a book designer, mostly because doing it yourself doesn't work - it may look good to you, but it doesn't look good - and the vast majority of ready-to-publish covers on sale online are just appalling and are really taking advantage of self-publishers (seriously, they'll charge $100 for something worse than what you've made, and complain that folks like me are charging $150 for professionally made pre-made covers). At the very least you could explore finding a real book designer, get some quotes, before you fall to DIY covers. The idea that you cannot afford it doesn't mean you can't speak to us. Many of us have low budget clients on the side or out main projects and we don't bite.
Otherwise, keep it simple, don't fall on cliches - especially in type - don't fall back on trends that will get tired one day, and don't shirk type as it is by far the most important thing you can put on your cover.
Edit: I came back in to this post due to a notification and saw something I hadn't the first time, first comment/third cover: why is the cover "designer" named on the cover? I'm hoping you don't use it because it's a pretty ugly thing, but any book designer who is trying to take the spotlight from the author is a charlatan. The credit for design belongs in the imprint - and wherever the author decides to sing their praises - their name should be nowhere near the cover. Even designers who write their own books - like Robin Kinross - don't state they designed the thing on the front, even they keep it in the imprint. Scrape that nonsense off, it makes the cover seem EVEN MORE unprofessional.