Lisp

I'm new to programming, and I've been learning Python and Fortran, the latter because it's part of my mathematics degree. I want to learn Lisp because it supposedly makes you a better programmer. Which dialect should I learn?

>>1
Mostly what >>3 said. Just read SICP (and R5RS) to learn Scheme and some important programming ideas/concepts/paradigms.
Learn CL if you want something more 'practical'/"real-world"-programming-oriented (in the sense that CL is made to allow a wide variety of paradigms and styles, as opposed to Scheme which tries to be much cleaner).