What's a good Rite of War for a new player?
... a wide question indeed, since that's totally subjective. A good RoW in terms of rules ? In terms of synergies ? In its capabilities to take Allies ?
Also, it entirely depends on the kind of army you want to play with your EC - do you like lightning fast jet-bikes all over the place ? Would you like to bring more tanks than in a usual list ? Do you prefer heavily armoured elite infantry / Terminators over normal power armoured troops ?
Those are all factors you can (but need not to, of course) figure in. Also, will they be traitor EC or loyalist ... etc.
The one advice I can give without you providing a bit more of a detail of the general idea your list should take, is to step very carefully when considering 'Pride of the Legion'.
That particular RoW can quickly become a trap for the unwary or inexperienced, but it can also offer you great benefits.