Hallo. 'Mir ist es egal.' Tim

"Egal" is of course the most common expression. I also often say "Meinetwegen!" (it's like "Whatever!"). Sometimes I also use the construction "Es ist mir [ziemlich] schnurz": Es ist mir [ziemlich] schnurz, was man darüber denkt, es ist mir schnurz, ob das teuer ist etc. However you probably shouldn't use this last one too much, it's not rude, but also not very nice.

Das ist mir egal!

If you mean to say "I don't care" and in, when someone gives you a choice and you don't mind either way, then you would say 'Es ist mir egal' or you could just say 'Egal' the short form.