Start reading UFF at iss 21 where millar and land started.That's where it really got good.The rest had terrible art which pretty much ruined the entire comic.
USM is really good.Some arcs were pretty lame,avoid -IRRESPONSIBLE-and -SUPERSTARS-.
Ultimates2 has been an Amazing ride.Ultimates1 was good,but not great.However Ultiamtes2 is superb.Wait till the hardcover comes out and purchase that.
UXM i only started getting at 55,where the longshot arc started and I perfectly understand everything.If your really intrigued by some arcs pick the trades up.If you don't just start at Magnetic North.All you really need to know is that Magneto was defeated and is being held captive in Triskelon.
UIM is a good read.Not need at all though.It all has to do with when Tony was a young kid,not much action,but a good storyline.
Ultimate nightmare and ultiamte secret are countdowns to Ultimate extinction,which is about the arrival of Galactus.
Ultimate wolverine vs Hulk is looking cool to,it has some pretty big ramifications on the universe,so I recommend it when it arrives.Plus,the writer co-created Lost.