hi,
good considerations. but, i prefer sr225's for jazz & vocals.
the akg 271-studio is a closed headphone, has minimal bass & excellent midrange & is a bit on the echo chamber side but are very good at blocking out noise, coming & going, & they will keep your ears warm in cold weather. the grado sr-225 has bass & mid-range but is an open phone & everyone will be listening to your music & much as you.
i would definitely recommend the sr225, for vocals & jazz & fun. i prefer the 225's myself in the sr60 to sr325 line.
imo, the sr225 would be a better choice for all music types vs. the 271. plus, they are a lot of fun to listen to with all sorts of music. be careful of buying a used pair of sr225’s due to grado grattle. a warranted pair will cover any inevitable cost to repair the grattle during the warranty period. extreme heavy bass use from prior owners can cause the grattle. however, grado will happily fix it in or out of warranty.
for more on grattle, do a search here on head-fi.
happy hunting.