There are definitely a handful that require Step 2 now and it seems to be more and more popular for programs to want to see your Step 2. I think it all depends on your Step 1:
1) If your Step 1 is really high, don't bother applying to the schools requiring Step 2, you'll probably do fine with interview invites (if you did well third year, have research, etc.). Then take Step 2 late.
2) If your Step 1 is middle of the road, probably better to take Step 2 early that way you can show programs you improved on your score. Also nice to just have it out of the way. You could go either way though with taking it early or late.
3) If your Step 1 is lower (but you have strong third year grades, letters and lots of research). Take Step 2 ASAP and score as high as you can. Shows you can improve and somewhat makes up for your lower Step 1
By rank time, I'm pretty sure just about everyone has taken Step 2, so it's more about taking it in time to report on ERAS/Interviews vs taking it in december or january. Hope this helps.