A few guys predicted this; (shout outs to CA Iverson and Olyy) I think the games are very, very different and they kind of do different things.
In terms of pick up and playability, RWC is the one to go for. Easy controls, basics well covered, can score nice individual tries from the outset. People can get the hang of it quickly (helped by most people having played the older games) so can jump in and get it 'working' quickly.
RC on the other hand is fairly frustrating for the first time users. It feels like half your passes go to ground, all your rucks get turned over etc. Given time though, I reckon RC is way way deeper in terms of gameplay. Phase play actually matters, you can generate quick ball and catch the defence before it is aligned, passing system makes sense now and you can score so many unique tries. I think the hangover from rugby08 has affected it negatively a wee bit (e.g. perfect passes to your backs, run on the angle then through the gap everytime, which doesn;t work at all in RC). You can't really apply a formula on how to score tries which I like, have to adapt and play it as you see it, eg people complain about passes from the rucks going to ground, most likely this is cause a forward is at the base.. got to adapt.
So I would say RWC = arcade, RC = Sim to a degree. RC computer controlled offloads are a bit overkill (sliders sort this out but it is a bit tedious editing them all).
Both do some things better than the other title in terms of gameplay, each have their positives and negatives.