I've been streaming the games online for 2 years now and league pass for 4 years.
2 years ago the quality was horrible. It almost wasn't worth watching some of the games.
Last year they really stepped it up. They completely re-tooled the league pass video player. The quality was better, and I had much less issues. The one thing that still would bother me though was that the audio and video would consistenly get out of sink and I'd have to reload the player to fix this problem.
I also had issues viewing archived games, they would take an absurdly long time to load, and then sometimes wouldn't even start at the beginning of the game. The broadcast would jump in randomly like say half way through the second quarter.
Overall, having done both, I still consistently enjoy watching the games through my cable provider. It's the ol' tried and true method. But, with advancements in new media occurring all the time it wouldn't surprise me to see the streaming video equal cable this season. That's the wave of the future anyway, sooner then later (say next 10yrs) none of us will even be talking about our "cable providers", and our kids will have to ask us what that even means.
I think you definitely want to be streaming on an HD flat screen (plasma or lcd)to get the SD cable feel. I was streaming on a 27in SD flat screen and even last year the image quality wasn't nearly as good as SD cable. It obviously depends on your computers capabilities and matching the settings properly on between the comp and tv, as well, but I'm pretty confident I had everything set up as well as possible.