Bajaj Avenger 150 v/s Bajaj V v/s suzuki gixxer :: Need Suggestions

Hi Friends.

This is my first post,

I am Planning to buy a bike. This will be my 1st bike. Since a long tome i am doing some researches and finally have shortlisted a few. There are multiple options going in my head:

My Usage : Daily commuting for work (50 to 60 Km per day), rarely long drives.

1. Since this will be my 1st bike, shall i buy new or take 2nd hand.
2. If 2nd hand, what should be max kms used and what is max amount i should go for? ( my preferred bike is FZ for 2nd hand : suggestions open)
3. if new than which one among these: Suzuki Gixxer sf / bajaj avenger 150 / bajaj V. ( 150 CC range with Mileage 43 and above :: Suggestions open)
( i understand suzuki is preferred bike but issue that i am facing is it will be difficult for my parents to sit on the bike because of the height, that is were avenger came in picture.)
4. Which bike cause less back ache, since i had slip disc earlier ( sports or cruiser)

I understand this could be a childish post but you guys are the one who can help me taking the decision since you all are experienced riders.

Thank you for reading the post. Looking forward for your feedback...