I have tried both Tivo and Navigator (TWC's DVR software). Tivo is awesome and Navigator is subpar. I used to have Dish 722 DVRs about 2.5 years ago now as well. IMHO, the Tivo interface is as good as Dish but different in a number of ways. That said, Tivo on TWC can be frustrating at times. The whole SDV (switched digital video) and TA (Tuning Adapter) hack can be buggy. I decided to return my Tivos before my 30 days ran out due to Tuning Adapter problems. I have since moved, and I am considering trying Tivo again. Recent Navigator issues have included:
Half Resolution video (intermittent)
Frequent Crashes (requires power-cycle)
Loss of recording capacity due to software bugs
FF and RW not responsive
In short, I recommend trying the Tivo. My local BestBuy has the 45 hour version for $79.99. Yours might too.
PS - I didn't mention all the things you might miss coming from Dish to TWC Navigator, like folders, 30 second skip, decent search, and a guide that shows more than 90 minutes.