This is my opinion on the bikes I have ridden/raced.
1) Lewis Bros KTM 74.5 GP 250 has won 3 Aus titles plus KTM won the world champs that year so its my pick.
2) VR Montesa light and fast but needs allot of input on the corners.
3) RH Suzuki blinding faster than anything else and light as but lacks brakes and usability.Moves around under power and wears you out fast , lights up fighting for traction.
4) YZ Yamaha , lighter than air and a great motor and has brakes to match. All the weight is rear ward and it turns like a plow if the forks dont flex first.
5) Maico MC 250 , slowest bike but you dont have to slow down much on it so it evens out.