I'd suggest converting the Same Song in 2-3 different speeds and Then Decide IF you hear a difference.
On certain songs I hear a tighter, more desirable presentation with 192 vs. 160 (not a big spread) but other songs are just fine at 160 (mostly Jazz & Soft Rock).
I've just decided to use 192 in the future and press on.
Storage space is not an issuee any more as GB are less than a $1 now days. So, if you are going to do it do it right the first time and go 256. My ears in my car certainly hear a difference between 128 and 256. You can go to 320 but now you may be hard pressed to hear a difference.
I have a mix of compression on mine. I have found that 128 is a little low on some albums (especially r&b type stuff), but that it is fine for most.
Also note that the album itself may make a difference. I have one album which has no headroom on the tracks, and just about any mp3 setting will cause it to distort. If I want it right, I am going to have to rip to .WAV and then edit the file before converting back to mp3. Takes a lot of time, so I haven't done that!
192 is best for in between, I mean if you have a big size usb stick then forget it and just go 256... it's no problem now since 16gb and up seems to be the norm, back when you could only get 1-2gb sticks or CDR's only then yeah, I would worry about compression, not so much now.