Gant is the better pitching prospect of the two. He is currently spending his second stint of the 2015 season with the Binghamton Mets. The Mets aggressively skipped the 22-year-old over St. Lucie after a strong 2014 campaign in Savannah. Gant struggled in his first exposure to Double-A baseball, and was sent down to St. Luice at the end of May where he dominated the level to the tune of a 1.79 ERA and a 48:10 K:BB ratio in 40.1 innings. He was promoted back to Binghamton earlier this month and has fared better this time around, although he is still more hittable than you would like.
I have seen Gant live a couple times and he showed some year-over-year improvements when I saw him this April for Binghamton. The fastball, which previously lived in the high-80s, was 90-91, and there were reports of even more velocity after his demotion to St. Lucie. That is still only a fringe-average to average major league fastball for a right-hander, and Gant's command isn't anything special, but when he is going well he is able to use the fastball to get ahead of hitters and set up his split-change, which is his best secondary offering. It projects as a solid-average major league pitch for me. He is throwing his breaking ball(s) more this year. He's tightened up his mid-70s curve some this year and he can spot it for strike one or bury it when he's ahead in the count, but I don't see it as a true swing-and-miss offering yet. It looked like he threw a slider or two in my April look as well.
You can squint and see a fifth starter profile here, but Gant struggles when he has to challenge guys with his fastball behind in counts, which is a pretty big red flag for me. Still, I have always liked the arm and do think he will pitch in the majors at some point. He was in consideration for the back end of my midseason top 20 prospect list, and if I went to 25 names he probably makes it. He was also a prep pick out of Georgia, so I have little doubt that the Braves scouted him heavily as an amateur, and maybe even specifically targeted him in this deal, given their predilection for acquiring talent from their home state.
When I saw Rob Whalen in Savannah last Summer, he featured a full four-pitch mix and would throw almost anything in any count. The fastball bumped 91, but was mostly high 80s, and none of the three secondary offerings projected to major league average. His ability to throw a variety of pitches in a variety of counts has allowed him to achieve a fair amount of success in the low minors, but his strikeout and walk rates have gotten worse at each successive level and he looks like an upper minors org arm in the Greg Peavey or Tyler Pill mold.