We had a 05,12.37 which was a fantastic van (fit in our garage too), although in bad weather it was a headache because there just wasnt enough room for us and to hang the wet clothing/towels.
we now have an 06, 14.44 which has a bed at the back and a shower and toilet, for the two of us it is perfect size, easy to tow and store and has all the comforts we need, we find the heater works extreamly well, however in damp weather it causes a lot of condensation on the cupboards which i cant imagine is good for the materials. The a/c also works well in warmer weather but not fantastc in extreme heat. The shower and toilet is great for bad weather as you dont need to leave the van, also if you have a little one those night toilet needs are made easier.
Both our expandas had regular flys, after a few runs we only put the flys out when rain was expected and found the canvas on its own was fine, the fly does however provide a bit more insulation, i imagine the waterproof flys would be even better. Out 12 had an annex we never used, now we have the 14 and a few things have changed we wish we had one and they are expensive so if you are looking at them and find one with an annex, even though you might not think you need it, it can be handy.
If i had a family i would go for a 16.49-3
we had a camper trailer between the 12 and 14 and missed the 12 every minute, hence the 14 was purchased after two trips in the trailer. The expandas dont get hot like a trailer tent, nor do they get as cold, you have less setup and more comfort.