Weaker mobs/solo, speed for sure. No harm in popping life for evasion debuff and swapping back to speed if the mob has particularly high evasion.

As far as NMs|high lvl mobs; given the low cool down on both, there's really no reason not to keep evasion debuff on as much as possible while still riding speed for tp generation. It's a good idea to snag some hate management abilities from ARC and keep some defensive abilities on the bar as well since you might snag hate here and there doing this. Hate is still pretty wonky sometimes, so the tank might have trouble grabbing it back.

tl;dr - Don't be a lazy LNC. Use both.