buy whichever motor you want, neither are really better then the other. in some aspects maybe but i say buy whicher you like better.
the 28hp figure came directly from malossi who are very well known in the scooter tuning world. the cylinder kit rcmax (stage6 race cylinder) used to use made 18 hp ( you can find dyno figures online ) . its not bs. under 71cc is just a my guess . 15hp for 100cc is way underpowered
alx makes a badass twin, just be ready to break out 4k + 2k for chassis upgrades lol and it wont fit losis