Welcome to the forums, riverview!
I use the 300mm f4 AF personally, and while IMO it's a great lens, it definitely has limited use. The 70-300 is excellent, and if you ever decide to upgrade to full frame in the future you have that option. Not to mention that it's very well built, and offered at a good price. If you want something a little faster you could consider the 70-200 f4, but you'll have to sacrifice a little range at the long end and dish out more than twice the cost of the 70-300. That being said though, the 70-300 isn't too good of a performer at 300mm anyways. It's usable, but not optimal.
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams