Eurotraveller,
First of all, in general I agree with all that has been said above.
Sure it is best if you can have one instructor, but two is not bad as long as they talk to one another or read one another's notes from your previous lessons before flying, (and as long as their teaching is not mutually incompatible).
If they don't, then it may be best to transfer your allegiance to instructor No. 2 entirely, or go to another school.
Give instructor No. 2 a fair try. He/she may not be 'John Popular', but with closer acquaintance you may find that he/she is a d**n good pilot/instructor and a good working relationship may develop that helps your flying. A less popular instructor may have more time for you. You may not want to go back to 'John Popular'.
Good luck with your training.
Broomstick.