1. Kestrels - all confed frigates are is slower kestrels with a little bit more shields and armour. Add the fact that the Kestrels all have fighters, an you've got an easy win for the Kestrels. There would probably be 2 or 3 Kestrels left at the end!
2. It matters - if they encounter each other at close range, the cruiser will win, becuase they can pound like crazy close in. If the kestrels jumped in from one side and the cruisers were at the other end of the system, it would probably be a different story. Overall? I'd say cruisers.
3. Cruisers - although Rapiers are a formidable enemy, and often hard to deal with from a player standpoint because of all the torpedoes, etc, there is a difference here: A player is a single target, but in this case you're dealing with 4 cruisers and 16 mantas. All the torpedoes go into the first target - boom, he's dead, 4000% overkill, but then the rapiers have no torps left. By the time they start strafing with their rockets, after missiles have decimated half of them, they will injure heavily all of them, but kill none of the cruisers.
4. Rebels. Two ultra-powerful, fast ships against 4 sitting ducks? This one's obvious.
5. Confed cruisers, unfortunately, becuase the destroyers usually strafe, and the proton turrets and neutron blasters on the cruisers would decimate them.