I've shared excerpts of my WsIP with my husband and with some trusted friends. I've shared a short story in SYW for critique.
I'll admit that ANY negative reactions from my husband, even the slightest hesitations before responding, tend to throw me into writer's block and writer's insecurity for days. But otherwise, I'm a feedback junkie. Pathologically so.
As for what's best, that depends entirely on the individual writer and on the prospective audience. My husband doesn't really write fiction, but if he did, he wouldn't want to share his work with anyone until he felt it was of publishable quality.
In contrast, I crave reader response, especially since I've only been writing fiction for a little over a year. I want to know if my writing is effective...if it "works." And if I'm making novice mistakes (too many unnecessary adverbs/adjectives...POV shifts...too much backstory, etc), then I want to know NOW, not after I've written a complete manuscript full of those mistakes.