I've had them both but passed on the 64 to someone else a few years ago, before getting the Oregon, so I can't do a side-by-side. And obviously my 64 was an older model -- 2005, as I remember.
I like the Oregon's display, but I'm not crazy about the touchscreen. It's OK, but the UI is clunky.
I think if I were going seriously into back country, I'd take the 64. It seems more rugged to me (but I can't back that up with anything except subjective feeling). But for day hiking or various tasks, the Oregon is excellent, and it does drop into a jacket pocket or fannypack very easily.
No matter which way you go, don't spend money on the "t" models. Excellent topo maps are available for free, on the web, and they're easily downloaded and installed. Legal, too -- so far as I can tell.