on my '87 blazer, 305, auto, my front hub locks for the 4wd seem to be stripped. should i get manual or automatic hub locks?

 

If auto is what came on it, then you should keep it auto.

 

Auto or manual, put on what you'll use. I use auto hubs on my daily driver 'cause I don't actually use the 4wd very often.
I put manual hubs on the orange '85 'cause I do use it for 4X4ing in the worst conditions I can find.
It's your choice and it's pretty easy to install either manual or auto.