Cable vs. Fiber - Knowledgeable Input Needed

This isn't really a troubleshooting thread btw, I need some expert input on a subject I'm not really familiar with

So currently I have my internet provided by Fios - 15mpbs up and 5 mpbs down. Today a salesman from Cablevision offered me an "upgrade" - 50mpbs up and 8 mpbs down. Now what I understand is that with a fiber optic network, what they advertise (in this case 15/5) is what you usually get. With cable the bandwidth is shared between people in your neighborhood, so one rarely gets that full 50mbps. However, there's so much conflicting information on the internet about this I'm not sure what to believe.

So my question is, should I stay with Fios or switch to Cablevision (cost not considered)? If I do switch, how much of that 50mbps could I realistically use with a cable network?

Thanks for your help.

One question I would ask is how many folks in the "neighborhood" have Cablevision.
Then you have to figure out is when you are on the computer. Is it in the morning, evening, or late at night?
Last but not least....are you going to get more noticeable bang for you buck by going to Cablevision?