Transgo/Transco . If you're looking for a performance kit without being excessively harsh, the Transgo kit TF-2. If you're looking for a kit that will improve the shift quality only, then go with the Transco SK-TF. I've used both. I lucked out with the Challenger using the SK-TF. The builder that put in in had a couple of tricks up his sleeve beides just the shift kit. Normal driving, you felt the improved shifts. Slap the happy pedal hard, and it shifted like you had the big kit in it.
There are brands of kits that are available for sure, and many will tell you that such and such a brand is the best. I worked in the transmission parts industry for almost 30 years, covering most of Western Canada and the Transco/Transgo brand of shift kit was the kit of choice by builders by a large margin.