DTV:
There are lots of rounds, last one being Tincans. (Used to be 15 rounds, but a couple were added, so I guess 20 or so now) There are 3 waves in every round.
At the end of each round you get experience.
The more teammates stay alive through the round, the more experience you get.
The more bots spawn, the more experience you get (More players = More bots).
The faster you kill the bots off, the more experience you get.
The higher the wave, the more experience you get. There is a cap on how much exp you can get, but I cannot remember it.
That should be it really. Don't know the exact formular, but you get the idea.
If you have a decent team you can get lots of exp.
Always good to see DTV-Heroes like Pato, Illu, Jaeger, Cora, Mauler, Bob, Utter etc etc
Rageball:
Definitely a lot more fun if you have balanced teams.
Faster gameplay, so you gotta be fast
Agi whores are a lot more viable than str whores since running is the most important thing.
Also you wanna set your "free look" key to something easy to reach, since you constantly have to check where teammates are in case you get the ball and need to pass it away quickly.
As for the rules: Before Rageball was taken down for a while I actually remember there being rules. But now I cannot find them anymore. I think you could see them when joining EU6/NA6. But now they aren't ingame anymore either.
And yes, I definitely do remember killing people who are not near the ball was not allowed. (Ranged obviously being an exception)
Sadly too many people still go play TDM rather than try to get the ball and score a goal.
If you have a nice team, then you get lots of exp (Afaik it is not double exp like Battle or Siege, but not sure)
If you have a team of retarded windowlickers, then you are better off getting exp on another server.