I500T. I shredded up my first design multistage SEDS rocket on a i1299N-P last year. RSO L-3 dude called it sledgehammer. It was only three I500T peak thrust. You don't maximize thrust on lightest weight min diameter rocket. I pick milder motors now. Second rocket went with mild H's. This year's team let me pick motors for their project rocket. They picked CTI Vmax and prof laugh with had 0-M1.5 in 0.3s shredded flashbacks and said no then assigned Me to pick motors. Higher sim alts. Less G's. You don't need a bunch of thrust always. Sometimes you want a consistent push.
One flight on the I300T-14A single stage kit. Nice flame, very gentle on airframe. Nice build to peak then dropping off smoothly. It's not just a massive spike of activity and no smoothness. It's like a blue flame of CTI Classic, very predictable. Mild and bland but doesn't eat rockets like WarP9 might. The I 1299NP RMS was the loudest I motor I ever heard. I chose an H219T-14A for cert this spring. For now I avoid the freaking IMAX, Vmax, WarP9, and ST loads.