If its good looking hosties who are up for a laugh,cheap accommodation,and top nightlife you are after, then Liverpool it is!!
If, on the other hand you are after exactly the opposite of the above then Luton is the place to be.
That said,the flying is a little more varied at LTN i.e more nightstops,more destinations (Scotland / Athens) etc.
Oh,and forget keeping your hubcaps whichever base you choose!!
