Anythings better then the Axial engines, there not that great, just run of the mill rtr engines...
U dont need anything bigger then the 5.9, bigger isn't always better. A .28 sized engine has more then enough power for a monster truck.
LRP's are great engines, they're available in 4 different flavors so u can choose the right one that fits ur needs best.
Picco .28's are regarded as one of the best, if not THE BEST big block MT engines out there. Build quality is second to none... Billet piston, swiss bearings ect. made from super high quality materials, it's one of those "u get what u pay for" kind of things.
YouTube has tons of vids on all the engines mentioned in this thread, go check'em out!