I've got both, both are incredible but quite different.
The SV TW is imho the best all around baitcaster on the market. It excels for chatterbaits/spinnerbaits, jerkbaits, standard size T-Rig/Free Rigs, flatside/squarebill cranks, blade baits, and a bunch of other typical Bass lures.
The HD TW is an absolute unit of a reel, built like a tank. Has brass gears vs. AI in the SV TW, and has a larger handle and knobs vs the SV TW. This reel is made for "heavy duty" techniques. Jigs, larger T-Rigs/Free Rigs, A-Rigs, 1-4oz Glides, deep cranks, C-Rigs, etc. Packs a ton of power in a relatively compact and ultra smooth package.
Think of the SV TW as an all around normal baitcaster while the HD TW is a heavy duty, significantly more robust baitcaster.