I quit NetFlix's streaming service (still get discs from them) a year or more ago (don't remember when) because their throughput got so slow that I couldn't watch anything. Literally, it would stop every 30 seconds and re-buffer for at least that long.
I have two ways to watch Amazon Prime streaming:
Through the BluRay player & TV in front of the treadmill. It takes a minute or so to load and start, but the quality is excellent. Excellent resolution and never choppy.
On the iPad through the Amazon Video app. Videos start immediately but the resolution is crappy for the first minute or three, then clears up and is excellent. As above, never choppy.
Comcast has the absolute worst customer service but they tend to have the fastest speeds (at least around here until fiber takes over) Im surprised about the poor netflix quality and have to wonder if you have some other issues with your streaming. Have you ever run a speed test?
Im getting 89.52 down and 11.95 up. I only pay for 50 down and 10 up
using poor wifi could cost you speed as will poor wiring
I did numerous speed tests. I always had blazingly fast download speeds and very good upload speeds. I was not using WiFi: I was connected to my cable box by Ethernet. At the same time that NetFlix was unwatchable, Amazon Video was perfect. I cannot imagine any problem at my end that would affect NetFlix but not Amazon Video. Both were coming in on the same cable internet line, through the same cable internet box, the same Ethernet cable to my BluRay player.
As for Comcast customer service, where I live (maybe it varies by location) Comcast has the best customer service of any business I've dealt with. Whenever I've had an issue, I get prompt attention from a tech who speaks unaccented English and clearly understands the system. When the issue is at my end they talk me through the steps, are patient while my computer reboots if that's needed. When the issue is at their end they give me an estimated repair time and they're always well ahead of it. They never tell me to do irrelevant things like clearing all my cookies or running questionable programs to "fix" my computer. They're never reading from a rote list of crap as happens with some companies where you're talking to someone in India or China who knows less than you do and does more damage than good. And with Comcast I never have to spend 15 minutes talking to someone who clearly knows nothing before they'll transfer me to someone who actually does know about the subject, as I did with Amazon yesterday when my Kindle Paperwhite died.
Except for the issue of throttling NetFlix (which may be a possibility, but I do not know if that's what was happening, since it might have been an issue with NetFlix failing to keep up with sufficient bandwidth for the customer load at the server center serving in my area) my experience with Comcast has been nothing but excellent. Even on the measure of reliability, outages are rare and usually don't last long.
FWIW, I ran a speed test from Ookla just now. I got 58.85 Mbps download and 6.42 Mbps upload. I may never get the 89 Mbps download you get, but I get more than enough for the best quality of any streaming service I'm aware of.
I'd probably give NetFlix another chance if I actually wanted to watch anything they have that Amazon doesn't. Frankly, I'd rather read a book. Yesterday I watched half an hour of a movie. It was a fun movie, and I'll finish it today or tomorrow, but after half an hour I got tired of watching and turned it off so I could read my book instead.