I have had all of these - well kind of. I have had the old Vista and the new one is sat here looking at me waiting for the Rumble Seat - but I have had a play with it before purchasing as a double.
I wouldn't worry about the seat sizes on any of these. They are all good sizes. If anything the Peach works out as having one of the biggest seats simply because the hood moves up the chassis as the child grows, whereas with the Geo and Apple2Pear (A2P) the hoods are fixed.
I have had many pushchairs with air tyres. I have slimed them all and I have never had a puncture.
This should help you re fold and seat size for the two iCandy's. The Geo is incredibly neat folded - everything nests together. The A2P folds as a one piece. It seems huge, and it is huge, but it is also handy. It can also be folded in parts or with one seat on, so there are options. The Peach Blossom is lots of pieces, but for some people these are easier to store and handle eg in a smaller car boot.
Bumper bars have never bothered me. In fact I usually take them off as they get in the way when putting an older child in and out of the seat. I personally prefer a leg rest for a little one, however, all of these are bucket seats and do tilt, so it wouldn't put me off either.
The A2P is very light to push. The seats are supportive even without the footrest. The hoods are fixed and a stretchy lycra type fabric. You lose basket space in tandem mode which for me is an issue. However, if you need something like to push, then this would negate the negatives because there is nothing else like it. Lovely to use. Folds as a one piece or in pieces.
The Peach Blossom is one of my favourite tandems - partly because its just beautiful to push and use. It's heavier than the A2P to push but its much more for your money quality wise - this is reflected in the price. Although the basket access is restricted, there is still a fair bit of basket space. I would absolutely have another one. I love the Peach as a single pushchair too - its probably the one that is still a neat single.
The Vista is great in that you get practically everything in the box for two, and you simply need to buy adaptors (only a small sum of money) for a baby and toddler set up, and you can decide if you actually need the rumble seat later. Everything interchanges nicely. I am less sure about the options once the baby reaches 6 months if they fall asleep and they need reclining. I think there is only one configuration where you can get a deep recline (both seats parent facing with the baby underneath) but I will stand corrected. You will be able to get a partial recline with both seats forward facing. The Vista basket is huge and accessible.
The Geo - I have to say the quality is superb and the ease of use is excellent. There's no adaptors or add on parts which is bliss compared to the iCandy's. However, the carrycot needs to be taken on and off without the baby in i.e. you can't get home and take the carrycot off with a sleeping baby in. I am also not sure about the lower seat because it has a 'bent in the middle' seat if that makes sense, and this seat is much smaller than the main seat. So you are unlikely to be able to swap the children around, which is handy as the children get older. You need to buy the side panniers for storage in tandem mode, but the single mode basket is huge.
Push wise, based on what I know...I would suggest that all of these are similar to push. The A2P is the lightest, but I need more experience with the Geo and I need to use the new Vista. The old Vista was fine to push.
My questions would be:
First of all what is your age gap?
Where do you go and what do you do? I would think that all would cope with canal pathways.
What size car boot have you got?
Where will the pushchair be stored and what would suit you, bits or one piece fold even if its large?
Do you need basket space, and if so how much eg just a changing bag and coats, or for shopping, picnics etc.