I actually don’t have one with Warlock as the main class! I love debuffs/CC, and trying to get my spell DC as high as possible means staying in the class (and short rest spell slots).

Whenever I multi Warlock it tends to be in martial builds, getting the extra attack with Pact of the Blade, or a quick dip into it for Mortal Reminder. I have a crit build I do this with.