Do you have that issue of aggregation/degradation with FIOS?
Well, ultimately you have it with anything. But FIOS has one large advantage in its favor - the fiber infrastructure being laid for FIOS is all net-new infrastructure over the last year or two, and therefore is designed and engineered much better than most existing cable OR telco-copper infrastructure - and is also in a much better state of repair, obviously - which should translate to greater speeds AND greater reliability. Of course, fiber into your home is also DAMN fast. Now, will you see much of a difference on your 16Mb or higher FIOS connection than with a good cable connection like my 8Mb service here? Maybe, maybe not. With a new, fast computer, my 8Mb service basically results in websites "snapping" in within a fraction of a second when I click on a link (unless there are delays with the site itself - like Avsig often, unfortunately), so that there's already not a lot of room for improvement in that user experience. And when I download files, I'd say there's not 1 in 10 sites that can provide a feed that maxes out my 8Mb pipe here, so you wouldn't see a huge improvement there either. But "aggregation/degradation" issues can actually start within your own home, potentially. If you're doing multi-tasking web access things yourself, or more likely if you have multiple family members simultaneously surfing and downloading files, that's when you'll potentially start to see a big difference with FIOS. If, for example, you're downloading from a site that can feed you at 5Mb, and at the same time your wife and your son are doing the same thing, you still haven't maxed out your pipe with your own household "aggregation" where my service would be showing "aggregation" issues from within my own home with that example.
Now, having said all that - if FIOS is available in your area, and its reasonably price competitive, then its clearly the best choice in terms of both speed and reliability, I'd say.