Its up to you if you want a faster processor ( 1ghz to 550mhz ) ( The milestone can be overclocked to 1.2ghz ). More ram ( 512mb to 256 mb ). If you want sense or vanilla android. If you want on screen keyboard or physical keyboard.
As for 2.2 on milestone [IMAGE] MotoFrenzy (Froyo 2.2 for milestone)
flash this i have been using for 2 weeks now safely and its amazing. If you haven't rooted your milestone yet then you don't know what your missing. It is the single best thing you can do to your phone. Once you overclock it everything becomes smooth as butter