Picture Quality is one good reason. It's better than what I had on Charter, Comcast, and Dish.
Price could be another issue depending on how much you're paying and what you're getting now.
Although I am disappointed because it seems the pricing is becoming less and less competitive. In other words I see the current pricing as ending up very similar to what the competition is offering instead of saving me money once my one year bundle it up. And where Verizon falls short is the capability and pricing on their HD boxes and DVRs. Wish they would rethink this because its expensive to be an all HD household due to this.
All companies have different pricing strategies. For example, CableVision charges you extra for VOD feeds... and if you want premium channels, it costs you a small fortune on CV - and yeah, they charge you EXTRA to get the VOD for your premium channel. In contrast, Verizon includes VOD with the channel. And premiums are a bargain compared to other services. If you get the movie package, you get some 47 SD channels (TMC, Showtime, Starz, Flix, Encore, IFC, Sundance), all of their HD counterparts (although Verizon, for some reason, still doesn't carry Starz West HD - but it's the only HD premium that they don't), and all of the VOD for those channels for IIRC $15/month. I still only pay $13/month for that package because I'm grandfathered into the lower price.
I've never had CV, but in general, here are the pros of FiOS, from my perspective:
1) The best PQ going. They're the only service that provides feeds, SD and HD, without doing any additional compression. And it shows.
2) Lots of channels - currently, per avsforum, FiOS has more HD channels than anyone. And they have a boatload of SD channels too.
3) Their internet service is just amazing - no slow periods (I get my full speed any time day or night), no throttling and no caps. It's just rock solid (I've had one minor outage in 3 1/2 years of service).
Some of the downsides:
1) Pricing is less flexible than other services. They have 2 basic tiers - Essentials and Extreme. Extreme gives you just about everything, but if you want HD, you really need Extreme. They really don't have tiered service. So if you want HD, but you don't want all the channels that they offer, then you're outta luck.
2) Billing - while it's gotten better, Verizon's billing leaves much to be desired. Although, personally, I've had very few issues - a couple very minor billing issues which were quickly and correctly resolved.
3) Because of an exclusive carry contract, MSNBC isn't available on FiOS in CV areas. CV has an exclusive carry contract - not sure when that contract is set to expire. And Verizon is currently fighting with CV to get MSG HD and MSG+ HD. If you're a big sports fan in the NY area, then this could be a show-stopper. The FCC is currently engaged in that process, and hopefully will find in Verizon's favor.