Coffeejoe

Thank you. I went ahead and bought the 15" one.  

Yes, BTWR shows both the 771g and the 701g available with SMA Male and SMA Female connectors, plus bnc.
https://www.buytwowayradios.com/nagoya-na-771g.html?___SID=U

That's one nice bonus of the 701...with the flexibility, it's a bit less in the way than even most factory antennas at the same length, though I wouldn't say it's enough to be worth replacing just for that.
If you need a replacement anyway, though, like a couple of mine have...

With the 15" antenna, clipping the radio on a belt can be a bit of a nuisance. The antenna seems to be in the way a lot. That's not the case so much with the shorter antennas.
If you're putting the radio in, or clipping it to, a backpack, that's not much of an issue. I would recommend considering how you'll use it to help you make your choice.
Another consideration is if you're using the radio in a vehicle, you might want to get a magnetic mount UHF 450 - 470 MHz antenna with the appropriate adapter for the radio. With that and a "speaker mic" plugged in, you can clip the radio to something in the vehicle cabin and use the radio as a mobile unit.

Comet, Diamond, Nagoya are just a few that make replacement/upgrade antennas.

Get the Nagoya NA-701G (5.5") and the Nagoya NA-771G (15.3"). Excellent antennas. And yes, the 15" does work better. I like it when hiking, placed in the bag with the antenna poking out the top.