I wouldn't use a line-lock at the strip except for the burn-out. I'd expect a high-power engine coupled with sticky meats to simply slide the front tires and cause a red-light.
If you've got a serious motor and converter, get the trans brake.
Trinity_gt gave good advice. Ideally, you'd want both; line lock for the burnout, and trans brake for the actual launch. If you can only afford one, get the trans brake.