I have a 10 ton press in my shop and it has done everything I have ever needed. I built it with a OTC ram and foot actuated air/hydraulic pump.
I have never used the inverted bottle jack style, probably because I always thought they were a compromise to a "real" press. There are tons (pun) of them out there so they must be OK.
I stuck in a link to a Grizzly unit that looks nice. It is more expensive than the Harbor Freight items, but a shop press is one of those things I wouldn't buy from HF.
My press has a gauge...a nice feature as it is sometimes difficult to feel when a "press" is home...no longer moving. You will see the gauge start to climb but the item being pushed isn't moving.
A 20 ton press has lots of oink...more oink than the Chinese frame can handle. If you need 20 tons, you need to take it to a machine shop.
Don't forget, heating bearings and gears to assemble is the preferred method..not brute force. A hydraulic press has a place in the shop, you have to know when to use it and when not to. Happy shopping cujo8.
http://www.grizzly.com/products/item.aspx?itemnumber=h6232 Stuart