A thousand times this. Last year EA Sports and DirecTV ran a promotion: buy Madden 25, get access to Sunday Ticket online. Among the devices I tested, it "worked" on Mac, PC, PS3, and iOS. MLB.TV is favorite product in America. It's ubiquitous, the streams are impeccable, and the things like multi-game views, "Park Only" audio and the ability to sync the radio and TV broadcasts are cherries on top. The ~$130 I pay for MLB.TV premium is money I happily pay each year.
Sunday Ticket online is the complete opposite of that. The servers are always full, the games are 5-10 minutes behind Twitter and the radio, and even when you can get on the picture is crap and unreliable. Even though I had access to it for free, by week 4 I was back at the bars watching games. Any time I was back home and thought I might throw on a game just because, it wasn't worth the aggrivation.
Until NFL and DirecTV step up their game, my advice would be do not buy. It's not worth the minutes you'll spend swearing at your TV each week for missing football.