I have a TIVO XL4 and a FIOS 7232 sitting side by side and interchange between them. I would give a slight edge to TIVO only because I like their HD interface better.
If I had to give up one or the other, however, it would be the TIVO with VOD as the game changer.
In terms of basic functionality like recording, scheduling, playback, reliability, sound and picture quality, they are a wash. TIVO guide data is better, but FIOS has improved IMO.
People manage their DVR's differently. What I like you may not. What I dislike you may not. As previous posts indicate, you can make the change to TIVO rather inexpensively. Give it a try. It's not a lifetime commitment.