IMHO - You can put any size you want if you are using the premium feature. This may also depend on your site design for sizes. Usually bigger sizes for premium since they are paying for the perk. If you are not using premium then leave it as is. :)
Here is a tidbit regarding standard banners...
I searched but really could not find answer. :)
In the featured_member.html adding some custom join tags and even trying the join language tags plugin will work fine when displaying any of the ranking/details pages. No issue there.
They don't work when placed in the featured_member.html when...