Probably depends on where you live. I had Gigabit Fios at an apartment in Ballston and it was fantastic. Stupidly fast. No problems while I had them, so I can't speak to their customer support.

Xfinity has been a nightmare -- partly because their upload speeds are garbage, partly because they use some godawful broken throttling algorithm, and partly because their customer service strategy boils down to "beat up the customer with bots and phone trees until they go away".

If you have the option, go with Fios. If you get stuck with Xfinity, start at the gigabit plan. Anything less is unusable because of how bad their upload speeds and network mismanagement are.