For the small difference in price you won't regret going for the 20 ton. You never know when that little extra bit of ability may be necessary.
Be aware that there are (or at least were) two different models of the 20 ton press, both at the same price. One is gray, the other is orange in color. The orange one has a welded frame and some very cheesy press plates, while the gray frame bolts together and has much better press plates. I highly recommend going for the gray one.
I have not yet added the air powered jack to mine, but I've got it on the list along with a foot pedal control valve so that I can use both hands when necessary to hold an object or two in position until the press has a good hold on them.