As someone who has used the internet stream and PS3 stream, I'd have to say they're pretty similar. I had the PS3 last year and year before and I'd say it's like watching a really good SD picture, MOSTLY. Sometimes the quality would drastically shift and it would look like watching a RealVideo full screen, but I'd say 95% of the time it was the good SD picture. Now I haven't used the computer feed in about 5 years but I recall it being pretty decent as well. Fact is you're not going to be getting HD quality streaming using the apps or the PC feed, but the point of the streaming options are to be an accessory, not your primary way of viewing NFLST. Now, for us it WILL be, but then again we're paying less by not having DirecTV at the same time.
As a 49ers Fan, NFLST sadly is a way of life for me. Granted this year I could probably get away with not having it for the most part because my team is good and thus are being shown more nationally, but then you get scenarios like week 14 where the 49ers face the Seahawks, which will likely have MAJOR NFC Playoff implications. But no, in my market they'll be showing the Giants VS The Chargers. I'd rather watch vomiting in slow motion than watch that.