Get BF3 now and buy RO2 when TW or a modding team fix the gameplay if that will ever even happen. Frankly I would recommend getting RO1 over RO2. BF3 in hardcore mode will probably be equaly 'realistic' as RO2.
Exactly my thoughts.
I played the BF3 beta three days straight until they shut it down. I've played RO1 a week straight and even joined the 29th with the Darkest Hour Mod, what a great game (RO1). Playtimes 8h each week.
While playing bf3 i often had the feeling, that RO2 tried to copy the mainstream elements of bf3 but failed. The suppression in RO2 feels not right, in bf3 it feels right, because you know its a game aspect, it doesn't have to be real.
The sprinting in bf3 feels right, because thinking as a game aspect its perfect. In RO2 it just feels unreal.
My opinion is, that TW tried to mix the realism of RO1 with pure gaming aspects of BF3. This failed. Stats failed. Most of the time this failed attempts at pushing it more towards a COD/BF3 gameplay shine through the game. This kinda ruins it for me.
I love RO1 and i love BadCompany2, they where not comparable.
But now, RO2 _IS_ comparable with BF3 and it fails in nearly every aspect in my eyes.
BF3 has gone the other way, they gone slightly more into realism which was done very well.
Now its for the mods to push RO2 back in the realism mode, where it hopefully will outshine BF3, making it into another subgenre of ego shooters, like RO1 was.
BF3 is a no-brainer, it just will be major fun.
RO2 depends on the future of development and mods.
But you have to consider, that all the new mainstream features TW tried to bring into RO2 was their first attempt. DICE had a LOT of experience beforehand. RO3 will contain this new experience, which TW had aquired with RO2.
So long story short, go for BF3 if you are unsure.
RO2 will probably be great with the incoming mods and future support from TW.
RO3 will be a perfect RO2 ;-)