I've used the Snap-On one only. It seems to work just fine. I've heard the gear puller in the Miller kit is better (I think it was Joe Donnelly that mentioned that).
With the S-O kit, I'd recommend putting a washer under the bolts on the puller. The gear on my truck was really stuck on tight and the bolt head began to chew up the plate surface as I tightend them down.
Either kit will do the job.
-Jay