Go with 2 x 2 seaters if the following conditions are true:
- You can haul 2 separate units easily, you'll need a pretty big trailer and truck
- You can store 2 separate units, I know a lot of guys get tired of storing units that don't used, will you be able to deal with a 2nd machine that sits most of the time?
- Your wife (or perhaps and older child) like to drive regularly
- Money isn't a big factor as price, maintenance, and accessories will cost double
Otherwise, just get a 4 seater and save some hassle (and money)
I have a 4 seater because I have 2 kids, but like Graniteguy, Im solo in it 95% of time. But... at the same time, I can't justify the cost of 2 units, nor would I enjoy having a 2nd unit that sits around most of the time, so a 4 seater works well for me and hasn't disappointed me despite what I "think I want".
Biggest downside to a 4 seater is not its size or cost or anything, its that nobody likes the backseats, even kids, especially on long rides. Front seats are just more fun.