My monsters currently are:
Commando: Prototype Behemoth - Just insane strength
Commando: Chichu - Not maxed out yet but already at 900 strength.
Sentinal: Silver Chocobo - With 8000 hp and some good abilities the Silver chocobo makes a dominante sentinal.
I'm currently working on getting other monsters to build up and finding some good monsters to infuse with.
I guess I'm going to have to be that guy and say my favorite enemy on skyrim is the guards. There is nothing more satisfying than (*spoiler alert*) transforming into a Werewolf and just harassing Whiterun or Riften.
My advice is Take off the intercooler. I had a friend who used the intercooler and it caused his 360 to red ring all the time too, but once he took it off it was fine. Just keep your xbox 360 in a well ventilated area and occasionally make sure the vents are filling up with dust or anything like that and you should be fine.
Source: True story.
The only reason I can think of to why you can't rent it is because they someone has bought their last copy and Gamefly has not acquired another. It was on the original xbox almost 10 years ago so it is for sale.
Source: I own both KOTOR games.