Tractors are like garages. Nobody ever complains about them being too large.

The reference to tractorbynet is spot on - there's more info there of value than anywhere else I've found. Still, HP is but one consideration, and some would argue not the most important. Of equal or greater value, is the frame size - which as a rule of thumb, will determine the strength of the hydraulically actuated components.

For example, I've a Kubota 3130 - has a relatively wimpy 25-ish HP at the PTO. It suits my needs, and for the rare occasions where I could use more HP (mowing wet/tall weeds on hills, tilling deep when dry), I just slow it down. However, I purposely went with this model over others that were similarly priced in the 35HP range, as they had smaller frames resulting in reduced loader capacity. You can make up for less horsepower on the PTO side of things somewhat by modifying how you operate, but nothing will make a wimpy loader lift more...

Doing it again, I'd definitely go used. These things are tanks - it takes a ton of abuse to ruin them, and plenty of lightly used examples are out there. For most folks, HST is the way to go...I'd never go back to manual after using it.