AIFF is a complete waste. It gobbles up your hard drive and you get nothing for it. Either use the Apple Lossless Encoder or AAC 256 VBR. You won't have any problems with either of those settings. They both sound the same. AAC is better for use with ipods and ipads.
There's no reason to convert iTunes downloads. They're already AAC 256 VBR. Leave em as they are.
It might help you to google basic info so you know how iTunes works.
I'm not being sarcastic...
I know how to use Google. That said this is an opinion forum and I was asking for your opinion. I wanted to know what method you used.
On last question, I think you'll tell me they are the same..... The thread is titled 320 Mp3. Wouldn't I use that? Perhaps I should google that one.
I appreciate your time.