Personally, I'm not enamored with deepstriking Stormboyz. I like that they got the ability, but in my mind it's got a niche use, for situations where you wouldn't just want them rushing up the table. If deepstriking is the way to go, kommandos are the way to go, in my opinion. That said, I do like Stormboyz because they can be across the table in a turn, in a similar spot to a Da Jump'd unit.
With that in mind, size 30, so you can absorb casualties and control the board.
Also, I use washers under my bases, and have 0 problem with anything standing up on 25s.