If you have a Mac, DO NOT use AAC. AAC is compressed. Use Apple Lossless for the best quality.
I would recommend Apples non-compressed format, AIFF, if you are on a Mac. Also MAX software has vigorous error correction (discussed above) which will take longer to rip with, but is the best guarantee of bit-for-bit rips. I don't think the error correction in iTunes is as good. I've had disks that MAX takes very long to rip that iTunes seems to blast right through with error correction turned on. External drives/transports may be slower than internal, even if both drives share the same specs, depending entirely upon the interface they have to your computer. I think the software's error-correction will be more important than the drive (someone correct me if I'm wrong).