Long time Landy nut here - although our 110 was nicked before Christmas (long topic on that somewhere). Basically a 90 is tiny in the back, if you have family too forget it. I've had various SIII's, 90's, 110's, Disco's down the years and the 110 is above all the best all round utility Landy. We've had 14 people in ours or 4 people and 4 bikes inside or 4 people plus all the holiday gear/sib/engine etc. The only way a 110 suffers is in being a little less capable off-road (more extreme stuff).
Having said that prices for the best Landy's (last of the line 300tdi) are pretty silly now. Our '98 CSW was worth about £10k when nicked. We replaced it with a 300tdi Disco - and seriously this is one of the best Landy's I've ever had - same 300tdi engine, same 4x4 running gear/chassis/drivetrain but stupid cheap at £1100 (with years mot - don't buy without one as all these old Discos' die due to MOT/corrosion failure being un-economical to repair). So nearly 1/10 the price - sure it's not a utility Landy that my heart loves but the early Discos are near classic now and it came with 2" Terrafirma lift, snorkel, HD bumper, erg mod/pump tweak, full leather, tons of room inside for family and gear, so much more comfort, 30mpg+ average but goes like a train - nicely battered and scarred bodywork and now with steels and MT's is as good off-road as my old ex-MOD 90 softtop.
The 110 is not that long really, all Landy's look bigger than they are but are narrow and a 90 is the same length as a hatchback. However, the space is set up differently in a Disco - *much* more legroom for the rear passengers (second row 110 seats are really kids only except short journeys) and less boot space (100" wheelbase of course) but 2/3 split seat work great so you can still carry two out back and loads of gear. Or if only two of you fold down the back seats.
Sadly biggest issue with owning a Defender right now is not having it nicked - epidemic rate of thefts and the No 1 most stolen vehicle pro rata numbers out there.