I'll try to help and remember my thoughts this January when I ended up picking Smugmug.
Pbase gives you a set amount of storage space and unlimited access to it.
Smugmug gives you a set amount of access (downloaded bandwidth) each month and unlimited storage.
Almost all of what I post is here on Nikon Cafe. Since the group is fairly small, there is not a lot of bandwidth used for each post. I don't post a lot, but could certainly post 6 to 10 times as many photos here without hitting the monthly limit. I have a lot of photos there (and a bunch more that I need to get up there) and not a lot of lookers, if the situation was reversed, I might have picked Pbase. Also I don't have to worry about the file size of my uploads (except I am still on dial-up-ugh!)
For what it is worth, you can get a $5 discount by entering an existing members email or code and they get a $10 credit when you do. Our founders, Frank (Flew) and Patrick Bramlett, are both Smugmug users so I used Frank as my reference since they are doing a lot of work to make this site what it is. If you happen to pick Smugmug, I suggest you pick one and do the same.
Hope this helps,
Bob