trusting that you have the spare wheels at 21" and 18" i would say that a MX front won't do you ay harm and the michelin S12 is the best. it's all i'll use. for the rear, well that's a different story and others can advise you better but the kanga lasts for ever and a day whilst the best enduro tyre on a four stroke, for me, is the D756 Dunlop.and again that's all i use (ok i use other tyres, regret it and go back!).
Taffy