As a longtime MST3K I'm enjoying both Rifftrax and Cinematic Titanic, though I'll echo the warning that Rifftrax is NOT MST3K. For a more conscious attempt to replicate MST3K stick with Cinematic Titanic, though for my money the Rifftrax are a better bargain. Though if Cinematic Titanic Live visits your town it is not to be missed!
I tend to like the Rifftrax of terrible recent Hollywood films rather than the fanboy flicks. I'm sure their Star Wars/LoTR/Spider-Man series sell better so whatever pays the rent. Crossroads, Next, Cloverfield are all favorites, wish they did more ridiculous films like those or The Day After Tomorrow though they've started focusing on that genre again with Twilight, The Room and Red Dawn (with Joel McHale). The shorts are uneven though their best efforts are easily MST3K quality, Harm: Safety Hides at Home and Drugs Are Like That are high points. I'm way behind on my shorts though.
Patton or PFT would easily slot into guest-starring on one of these, they'd just need to find a movie everyone is comfortable with. PFT takes on 10,000 BC? Patton and the latest X-Files movie? The more ponderous the better!