This is certainly not "expert" opinion, but here it is anyway.
I used a free site for a bit - Kodak ImageStation, I think (I suppose I should see if my stuff's still there and get rid of it if it is...) - and it was awful. You get what you pay for, I guess. Very little control of appearance, small image size, totally cluttered with ads. Yeuch. On the advice of several friends I moved to pbase, and I'm very happy with it. There are a few stupid things about it, and for a while there it was misbehaving a lot (not allowing uploads, stripping exif, etc.) but lately it's been fine. For the small fee it's a huge step up from ad-infested free sites. If I were you, I'd go look at a bunch of galleries on the sites you're considering and choose the one that suits your tastes. Good luck deciding!
Julie