Yeah, the hexar has a relatively slow top shutter speed so you probably want something around 100 speed for daytime work, e.g. Astia 100F or Velvia 100 or 100F. I prefer the first two- those are the two I've used most in colour autumn photography. You (probably) want strong but not unrealistic yellow and red primaries, so slide is the way to go. Other possibilities would be fuji reala or pro s or pro c or the comparable kodaks, but I'd stick to slide, as the 160 films don't render primaries as strongly IMHO, even if you rate the film slower than box speed. If you do go with print film then I'd say try reala 100.

I have some autumn slides that are really enjoyable when projected!

N.b. velvia 50 is yet another velvia choice that some may advocate; my results with velvia 100 have been more satisfying to me, but you might give 50 a try.