Not only size, but weight and whether the current tow vehicle can tow the Hi-Lo being considered which makes the smaller units more popular.
We have 3 adults (our adult son with DS adds that 3rd adult) and 2 larger dogs and find the 2310 doable for longer term, going on about 5 weeks and counting.
I guess what we have seen over the years is that people don't realize that if they are looking for storage space, a bigger trailer of any manufacturer won't assure that. For us, the swing-down bunk made this unit much preferred over the others. The next size up with the tip-out would not have been suitable. Can't do a lot with floor space.
To me, there is RVing and there is camping. We are campers so go smaller because we prefer to be outside when possible. Those that prefer to stay inside often seek larger spaces for their inside "toys".
Cathy & Associates (Alfred, Andrew, Rinnie & Yellow Dog)
2310 Hi Lo/2008 Ford Expedition