My favourite is the original Stargete: SG-1. My favourite season is season 7, but in general I prefer the earlier seasons. It wasn't quite the same when Richard Dean Anderson left. I love Atlantis too, but absolutely hated what they did with Universe. I hate the characters, and hate the camera style even more. I only saw a few episodes of Infinity, but it did not really show any connection with the live action show, so didn't bother watching it.
I loved all the live action Stargates, and I actually forgot Infinity existed, I always meant to check it out. Universe was my favourite even though I felt like they were trying to rip off both Battlestar Galactica and Star Trek Voyager. I loved the characters, I was so happy to find Robert Carlyle in Once Upon A Time after SGU ended.
My fave was Atlantis. I LOVE Rodney!. I know this probably sounds funny, but it was nice to see a Canadian character who is portrayed as very intelligent but also as an arrogant douchebag. It's a nice change from the typical 'very nice but not that bright' Canadian you see on most other shows.
I also really liked the cinematography and the sets for the Atlantis series.