What is the better way to join table for ASE 12.5?

To join table with T-SQL, there are 2 options:

select * from tab1 a join tab2 b on a.id = b.id where x=y

select * from tab1a, tab2 b where a.id = b.id and x=y

this is only a syntax difference or there is a performance difference? which one is better for performance?