What type of surgery is preferable--a laminectomy or a laminotomy?

Ussually laminectomy: Laminectomies are ussually preferable as this relieves the pressure on impinged nerves.

Depends: The goals of each are entirely different. A laminectomy causes more instability and removes muscular attachment at the level, but is a broad posterior decompression best reserved for severe central stenosis and bilateral nerve symptoms, whereas a laminotomy is a focused decompression. Totally depends on the pattern. For a unilateral nerve pinch a laminectomy is completely unnecessary.