I would mount it on the corner.

If its in the middle, then you will be hindered in your operations on what ever you want to do, as its always in the way.

In the end, you will have the space of the table for long pieces...

Now, if its an "old" huge vice like mine, I have it on the end. Then, my 8 foot of table space is free for my projects. I have mounted a light over the vice, so that I can see the "piece" that I am currently working on.

Even if its an old "wood vice", its generally still either mounted on the end of the table, or the corner.

You want your work bench as free as you can get it, to roam and not bump into things, that will "hurt" you, with sharp prongs or dull rods sticking into your body when you go "bump" as you work... (bruises dont make the job go easier :)...

I wish you well..

Jesse

try to mount it as far in as possible, without hindering operation of the handle. also take into account how strong your bench is. although you would ideally like your vise to the corner, to keep it out of the way, you may have to reinforce your bench to deal with the stresses you will be applying to your vise.

Hopefully, your bench is framed with 2X4s. You'll want to mount the vice close to the framing to support its weight. Consider mounting it with bolts--you can remove it when you want to use the space.

First, put it close to a corner, to make it more accessible. Second, make sure that internal Jaw is in line with the edge of your work bench, so you can affix a longer subjects vertically. Also, if your vice has a rotating future - make sure the vice lever will not be against your bench at different angles. Good luck