I have Flikr. Easy to link pictures to posts, but they recently introduced a 1000 picture limit, irrespective of image size. Having moved a load of photos over from PB and re-linked them in various forum posts, I find that I don't have all that many "free" photo slots left. Not enough to use my account as is for another big expedition post. Currently combatting this by creating collages, where I once would have uploaded 4 photos and posted them individually to a thread, I now do a paste up and upload a single image that includes all the shots I want to show. Probably not a problem for some time when you start using them.
Sadly, I think that it is largely a coin toss. Flikr cut its storage in the last year and folk that had over 1000 images were in a bit of a mess, unless they paid. Imagur had/has? a statement that they didn't want images linked to third party sites, which is the same language PB used when they wrecked the forums.
Any free service, when it gets big enough, over time, could change its rules and leave people in the lurch. That is just the gamble you take with all of them.