It depends.
The caffeine in regular Pulse makes it slightly more effective at boosting metabolic rate[1], strength[2], power[3], and endurance[4] than stim-free Pulse. If you want to maximize fat loss and athletic performance and tolerate caffeine without issue, regular Pulse is probably best for you.
If you’re very sensitive to caffeine, train later in the day, or prefer to get caffeine from other sources (like coffee and tea), but still want to take a pre-workout supplement that’ll enhance your performance in the gym, then stim-free Pulse is probably best for you.
1 http://www.ncbi.nlm.nih.gov/pubmed/2333832
2 http://www.ncbi.nlm.nih.gov/pubmed/17851681
3 https://jissn.biomedcentral.com/articles/10.1186/s12970-018-0216-0
4 http://www.ncbi.nlm.nih.gov/pubmed/16937961