i love u main tumse pyaar karta(m)/karti(f) hoon. I like u. Mujhe tum pasand ho/ tum mujhe achchhe lagate(achchhi lagati) ho u r great. tum bahot achchhe(m)(achchhi for f) ho if u want to use aap instead of tum, replace tum with aap and 'ho' with hain. Note: dont ever use 'mahaan' in this context, mahaan cannot be use as a direct substitute of word 'great'. Mahaan must be used only with really great personalities, or work etc.

okay your translation is here .. i love you : main tumse pyaar karta(for male)/karte(for female) hoon. i like you : muje tum pasand ho. you are great : tum mahan ho. have a nice day!!