How can I choose the best course to pursue in my under graduation after completing my class 12th?

For Engeneering & MBBS you should have good score in 12th standard and good rank in JEE or AIPMT. Otherwise you can go for B.sc & do Diploma in your interested feild.

Navin, the factors are: Own interest, type of work one wants to do after completing the studies, proficiency in academics, proficiency in practical work, Ability to be outdoors for extended hours, whetehr there is any intention to do business (own work) sooner or later.