As a relative newbie to the wonderful world of Rev flying ( only 2 years under my belt ) though have been flying dualies and power kites for many years .... I went into Rev flying and purchasing totally uninformed ( should have joined kitelife a long time ago ). I started with a Rev standard, followed closely by a full vent and although they both get plenty of flight time -it's the mid vent B series that's gets most of action these days - but What you go for is completely dependent on where you fly and the conditions you fly in .
If really want to cover yourself for almost all eventualities ( and fun flying ) I added a Zen and a B2 vented to my collection . Now I'm just holdimg off until I can justify matching Pro standard, mid vent and full vent .
Re availability in Germany - we have the same issue here in the UK so tbh I usually bring them over from Dave S at Huntingdon beach who always has a great range on offer and has some nice custom options which you just don't get over here .
Happy flying