i've got powertwin for when i need to go to tight shops and need it to go in boot of my 207 properly. it's great if you want a tandem. the options for the newborn/toddler are undelievable. you can have either in front or back
but i also recommend the twin two if you have a problem with 3 wheelers. as when dc get older you can have problems with sterring if toddlers falls asleep in front seat and leans to the side with powertwin. the 2 front wheels on twin two stops this. but obviously not as easy to swivel.
also get the carrycot/car seat that lies flat. then you can have lo facing you while laying flat in carrycot.
but i got an mb double earlier this year. it is the best, by far for walking.
i've had a loan on holiday of nipper double. it is also fantastic. but with 3 wheels on nipper and 4 wheels on mb, i'd prefer the 2 front sviwels anyday. much easier for going up kerbs.
mb is also very deceiving size wise. it looks like a huge monster i suppose. but it is actually smaller than nipper. and fits easier thru doors.
this is due to the mb wheels sitting directly under the seat units (only possible as 4 wheels instead of 3)
it has the biggest basket with very handy pockets/compartments for bottles/wallet,etc.
the raincover has a panel which opens at front (so too does jane) which is very important. as doubles get very very hot very quickly with raincover on.
both the jane and mb have large seat units. plenty of width . no problem with winter clothing and footmuff.
nipper is narrow. very narrow. struggle with a 2.5yo and winter clothing.
icandy has small seat units. and personally i dont like the full seat recline iykwim. prefer the back to move and bum bit stay in place. iykwim.
folding wise.
you will struggle to beat a jane.
one handed open. you just flick clip and "shake" and it springs open. and it folds up small. wheels pop off. but it's more designed to fit in a hatchbak shape wise.
mb and nipper fold like a penknife. they split in middle and fold in. very large. and very heavy to lift into boot (but not heavy to push or steer)
but if you have the boot space go for it.
icandy is also supposed to be huge to fold. not sure about mutsy.