which version shoud i use?

vB5 is having a bad press, it's very vuln and not very stable..

4.2.x is also vuln to multiple things, however it's easier to patch and not as many things to wrong.

If you're wanting 4.x.x, then go for 4.2.2 stable release or I think there is a 4.2.3 beta at the moment, not 100%.

I'd recommend 4.2.2 none the less.