I like RS 3, I just don't really like the New Interface System because my computer does not get along with it at all.
I'm looking forward to trying the Legacy beta and seeing if the interface change cures my woes. Honestly though I'd rather play EoC in the old Pre Rs-3 interface.
As for 07, it's great. I love 07. The player designed content is actually really cool (such as Rooftop Agility, which has actually made me enjoy the skill a bit).
07 just has that common feeling, and the community is pretty good.
Honestly, I'd just do both. Can't go wrong. The content is massive in RS 3, and I'll never complete all of it, despite being a player of 9 years already.
07 is great for familiarity and doing things the old way that you can't do in Rs 3 anymore.