Bugaboo offer 2 models of pram at the moment the Cameleon and the Gecko. the Cameleon being a bit more expensive of the two.
The Cameleon is the one I would recommend that is the one that is better value for money in the long run and worth the extra pounds.
The Gecko is alot smaller than the cameleon seat wise and my 2 year old has room to spare in the cameleon where as she filled and looked squashed in the gecko, so not as longevity to use compared to the cameleon. The handle on the gecko is quite low down and non adjustable so awkward if you are taller than 5'3". The sun hood is tiny and offers no real protection or coverage compared to the massive hood on the cameleon. The shopping basket is also not so big and would be filled just by the rainocver being in there wereas the cameleon basket is huge and expandable. The fleeces are non changeable nor do they fit on the gecko.
Summing up better longevity and space in the cameleon if you only wanted to buy one pram and the added extra features make the cameleon the much better option and not worth the saving as you can quite easily have the cameleon as the only pram from birth to 4 years (no fun buying loads of different prams- optional tho!lol) the gecko would be out grown by about 2-2 1/2 so additional funds would be needed to buying a new pushchair at some point for an older toddler.
I have had a frog and that is exactly an inbetween model smaller than the cameleon but bigger than the gecko. It has same gecko features.....