I'm going to go against the grain here, I would pick the 21i. I currently have a zx250 and fish a lot of docks. The boat manuvers fine in between them for me and I have yet to not be able to get access to something that a 20 foot boat would. Not saying it will never happen, but I have yet to see it. I also feel like my boat floats just a tad higher in the water because the extra length on it. That could be just my brain playing tricks on me, but I can get into some stupidly shallow places.

After fishing out of my boat for a few years, when I get into buddies 20 foot boats, I feel cramped. Plus, my front deck is just long enough that my wife can lay up there in a bikini during the summer. For that reason alone I don't think I'd ever buy another 20 footer. It's always nice to have somethign to do when the fish arn't biting.