If those are the only choice I'd pick the Spartan, that does not mean you should though. I would advise you try both on, so to speak, before you buy; is there a dealer near you? Cabela's? A fly-tying class? anywhere that you could sit next to and put your hands on them. or maybe another as well.
"What would be the difference?" about $110 depending on source. This discussion explains the major differences are size of knobs, levers and such; http://hmhvises.com/board/index.php?topic=115.0
largely a matter of tyer comfort, the jaws interchange, so either has the capability of large and small hooks.

I probably should not even offer advise on this anyhow, since I am still tying on the Thompson A from long ago. I saw an as new in the box A on the auction a while back and wish now I had bought it for a grand kid.

I also have a Spartan that I rarely use. It’s a well made piece of equipment that I purchased with a Midge head for very small hooks. However, I use my Regal almost exclusively, even down to size 20 hooks. It is easier to use, firmly holds hooks and has proven to be bulletproof. Roy

After going through several inexpensive vises, I purchased a HMH Spartan vise. It was the vise that my fly shop recommended, and I have no complaints. It is well made and does all the flies that I feel like tying.

The Standard is larger and a bit longer, if that matters. I have both, and the Spartan is cheaper and will do the job, but I like the Standard.

As with all things, it's all about personal preference. Best thing to do is try out multiples if possible. I absolutely love my Spartan. I tried a Regal a while back and while I love the jaws a little more than my HMH, there's a reason I still have my HMH...it just feels right to me.