I have been using vba-photopost gallery for 1 year and a half but recently I have problem with it and I just bougt photopost pro this week
(look at this: My feelings to photopost!
As I said in the thread above. Photopost is much better than vba-photopost-gallery in function. But, it is a little harder for you to install photopost pro than install vba-photopost gallery.
I do not use VBSEO
so I do not know about it but photopost pro work well with vbportal. I like its zip upload function and its control panel is also better than VBA. And one more thing is that you can install photopost and vbulletin in different databases.
The reason why I bought photopost pro is that I want to play with two and I feel that the support for VBA here is not as good as it was in VBA home page!(I have problem with it but noone can solve it yet).
There is one more thread a bout this comparision in this forum. You should take a look at this by searching.