You can not beat Yamaha or Honda for quality built bikes that hold up.
I'm a honda/yamaha guy.
2 stroke yz 250: awesome bikes, reliable. STuck to the track like glue. No front end push. Pulled hard off the start. (Got Meister a holeshot with a gate filled with 450's at the inaugeral Battle for Ohio race in 2013, and he ain't skinny
. ) Everything held up on that thing, except it's ability to run away from thieves.
2 stroke yz 125: Another awesome bike, raced it yesterday at the gp. Just super fun to rider, suspension is great, and the bike holds up wonderfully for a small bore pinger!
4 stroke yz 450: Suspension is second to none right out of the crate. Takes some getting used to for me anyway. I Need to stop riding it like a 2 stroke. I complain about how I hate it, but really in all reality it's just me. I changed up my riding style at big game on it and the bike wasn't fighting me any longer, it felt like we were riding in unison for the first time.
My last red bikes were 04 Honda 250F and 05 Honda 450F. I punished that 250F at the age of 17 weekly. It held up awesome, had about 200 hours on the bike with maybe 3 rebuilds and it pulled strong everywhere. 05 honda I had about 90 hours on it with no rebuilds and it was solid as well. I changed the oil in it after every 2 rides though. I think that really helps. Bikes love fresh gold oil........and a magnetic drain plug.