I'm not usually one to say it, but these are fairly simple questions that you should be able to find by reading and searching the site. So have a look around.
However, in the interest of helping the community as a whole:
Vacuum press uses a vacuum to apply pressure. Pressure is not as great and subjectively people probably feel the resulting product is inferior to pneumatic presses. Setup is cheaper and easier, but uses more disposable items.
Pneumatic press applies pressure using air pressure. More expensive. More time consuming to build and prob takes up more space (?). Pressure is higher so product should be lighter and bonding/durability better.
Clamp press is pretty primitive (fair enough? apologies to any clamp press people), but probably the lowest tech and therefore easiest to build. Probably the hardest to allow for even pressure over the whole ski surface.
Bottom line:
If you see yourself building a lot of skis then build a pneumatic press as long as you have the space, money and skills (or can pay someone for the skills) to build one.
Lower volumes get a vacuum pump.
Very low budget make a clamp press.
You will find most info on vacuum and pneumatic processes. I think graf snowboards maybe has better vacuum pressing info?
Heated pressing with the right epoxy produces a much stronger laminate. And also heat dramatically reduces the cure time of the epoxy so you can either produce a lot more skis in a given space of time or just that you dont have to have your press pumped up/vacuumed for as long.
Here is a prior discussion on your vacuum vs pneumatic
http://www.skibuilders.com/phpBB2/viewt ... ic++vacuum
And what montucky says below (fabric press) is also a great idea for lower volumes, but with the benefits of pneumatic pressing.