As the name suggests, I much prefer 700s/707s (don't freak out, they're not my favourite trains!). As someone who [unfortunately] has to use the class 345 trains every day, they're very uncomfortable trains and the interior design does not bode well. Grey, black and purple? Really?
The seats, particularly the longitudinal ones, are very uncomfortable. Whilst yes, the transverse ones are slightly more comfortable due to their high back, if you sit in the seats closest to the aisle, chances are especially during the peak someone will bash you with a bag every few minutes due to the narrow width of the gangway. Surely Bombardier/TfL could've thought to lay it out more like the S8 stock on the London Underground where the transverse seats are 'scattered' throughout the carriage.
The 345s are very hot and uncomfortable, lack poles or hand grips, meaning that if you are standing (which is very likely given the very few seats they seem to have) on the trains, you're going to get squashed and feel like you will topple over especially for the Stratford to Ilford leg of the journey.
Features like the PIS, air-conditioning (never does) and tail lights from time to time do not work, with the speakers receiving a lot of feedback when the driver comes on or 'glitching' out when the automated announcement comes on. Lack of information of the 345s PIS as well.
Whilst the 700/707 PIS may not be in sync with each other by a few seconds, they do a much better job quite a lot of the time. It tells you the full calling pattern of where the train is going, the time, information about capacity (and toilets on the 700s) on the train and more importantly live service information on the TfL network (something which the 345s, a TfL train don't???).
I've always been a supporter of both Siemens and Bombardier (I particularly thought the S Stock was one of the most innovative trains Bombardier has made), but I'm not as hooked by the Aventra as I anticipated. I think this round has to go to Siemens Desiro City.