I vote front-loader. We've been drooling over a particular set at Sears for about 2 years.
We 'got' the washer/dryer set the previous owners of our house had, and the washer is a top-loader. I'm not fond of it because the whole set cost $400 brand new.
: But then again, dh and I are total Consumer Reports junkies and research big purchases like appliances. No matter what you've got, you're going to have to tweak your washing routine for diapers. Plus the gals here are so helpful with suggestions, I don't think it would be a big deal.
My other point is that you're only going to be washing diapers for a finite time (unless you're aiming for a dozen kids), and after that you can be all about conserving water.
Oh, and with a front-loader you can wash your big fluffy bedspread at home instead of hanging out at the laundromat.
As for dryer features... make sure the lint catcher thing is easy to get out. The one in our current dryer is really annoying and not easy to mess with at all. It would be kinda neat to have that big dryer with the flat racks, hanging space, etc, but for us that would be overkill. A regular (but good) dryer would be fine. Plus our area is usually dry, so I've been going nuts drying everything outside (even my underwear).
Dh suggests lots of hot/cold settings (i.e. warm wash, warm rinse, hot/hot, cold/cold, etc.).