Pokemon Platinum which rotom should I get

[SecretCode]

what rotom should I choose

[Zidarose]

Rotom itself doesn't change, all the different form does is add in a new move for Rotom to use. Rotom can freely change between the various appliances, giving it a greatly level of versatility than it previously had.
The only thing I'd recommend is thinking carefully before using the Mow and the Oven Rotom forms as their moves drop your stats as well, at some point forcing you to switch to regain the lost power.