agreed with above. my vote would probably go to Mozart. pure magic.
Clementi really should be considered though. Beethoven was reportedly a huge fan of them. Prolly early Hummel too (simialr prob with classifying him as totally classical as he was like Beethoven, bridging to the romantic, though he was as adventourous with the content and transformation but rather experimented more with the form extedning it and making them larger scale works/longer etc.).