My boys (almost 6 yo and 4 yo) both have leapsters. They are great!
Don't quote me, but I was told that the only difference between the new L-Max and the original leapster is that the L-Max can be hooked up to the TV...other than that they are the same and play the same cartridges. You may be able to get a good deal on the original leapster as now it's "old".
Don't know anything about the V-Smile...don't think that was out when we got our Leapsters.
I guess I'd look at the titles of the cartridges that are out for each system and what ages they go up to (the leapster goes up to 4th grade right now I believe) so that you know it will grow with your child.