The RCA composite output will possibly be slightly better than the RF coax cable, but they're both relatively awful compared to S-Video if you have that. VHS quality of course isn't so hot so it probably won't matter a whole lot what connection you use.
Some video cards with a VIVO feature come with just an S-Video cable, but most come with an S-Video cable as well as an adapter plug or cable so that you can use composite. An All-In-Wonder card provides the S-Video/composite input as well as having a coax TV tuner. But they cost more than just a regular video card, so it'd be a waste to get that if you aren't looking to actually watch or record TV through it (and you can watch or record TV by watching it from the VCR with a regular VIVO card, just like watching on your TV set with the VCR). An add-in card like a PVR-150 is generally the best option if you actually want to do TV recording since it does hardware encoding, and it's cheaper than buying a new video card for no reason. It can also do the capturing from the VCR with pretty much any connector type.
External devices would work perfectly well for your needs too, if you have a USB 2.0 capable computer (which allows higher throughput so you can get better quality video). There are lots of them made specifically with this task in mind, so they come with software to make it easy for consumers to capture video from tapes (you can get them with an without the TV tuning feature). Many of the cheaper PCI cards also are focused on this as well as TV watching.