Welcome to Dakka Dakka.
The best thing to do would obviously be to try them out and see which you prefer or at the very least grab a copy or at least a look at each codex and see which one tickles your fancy.
I've played Orks for about a year now, very fun and quite diverse, although it is quite an old book it is very well balanced and a lot of fun to play and play against. Also it can still be pretty competitive if thats what you are into.
I've been playing against Space Wolves since my early days, although that was from 3rd ed onwards. The new Space Wolves book is quite powerful and makes for some interesting builds and army types. It has the balance and power of the regular
SM book with a lot of fun and powerful additions. Space Wolves have recieved their new book quite recently (year or two ago, I forget.) it's quite powerful and quite competitive also. Besides who doesn't love Drunk Space Vikings in Power Armour?
Whatever you decide, just make sure to enjoy it and have fun, also keep us posted and if you are looking for any help feel free to ask and to research in the forums with our extensive and helpful user base, the help you need is never far away. and not to sway your decision but......
Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.Orks.