Well, KTM doesnt make 4-stroke dirtbikes, so that's not an option.
Honda's are known for their reliability, although Suzuki usually have more parts available and a bit more effect. Yamaha is a good mix of both.
But I would even recommend the KTM, as it gives you so much more power and more fun. Yes, it's a 2-stroke, but its the best 2-stroke ever made!