Base and Type SH are exactly the same engine, transmission, body, etc., so I will list the differences specifically:

The Type SH has ATTS (Active Torque Transfer System) which uses hydraulic fluid pressure to transfer the torque between the front wheels. Sort of a pressurized fluid version of a limited slip differential, or posi-trac as they called it in the old days. There is a different alignment, slightly different suspension design, and a bunch of hydraulic lines running around the transmission. This system supposedly gives more RWD handling for a FWD car. I tested both when I bought mine, and could not find a difference untill I pushed it to about 90%, at which time the salesman asked if I knew what I was doing. They both use the same tires (Bridgestone Potenza RE92 205/50R/16). Other differences (not as important):

The Type SH has a standard trunk spoiler with LED, so there is no HMTBL in the back window.

Type SH rims are five straight spokes, cast aluminum but not polished. The base has five curved spokes, cast aluminum, polished surface. I replace mine with the Type SH rims..... look much better.

Type SH also has a standard leather wrapped shift knob, as well as courtesy lamps on the lower door pannels. In 1997-1998, the honeycomb grille was only on SH, then in 1999 they used it on all Preludes, replacing the two straight bars accross the grille section.

That should cover it. Any other questions, fire away!