If you are buying them for $40, then I suggest Pilotwings. Steel Diver is a bit hit or miss, and if you're spending $40 (or the equivalent of full price if you're not in the US) then I'm pretty sure gambling it on something you may not enjoy probably isn't the best idea.
PKMN Black: 0991-1032-9412 GT: LagunaGuy/3DS: 5155-2969-6127 Name: Ivan
I hear DoA is the most well done fighter on the 3DS. SFIV is a decent port (though they lost some stuff like the backgrounds animation) but not really more than a port. As for BlazBlue I hear it seems they made a real minimal effort, with problems like needing to use the awkwardly placed d-pad for controls and it not having online. Thus if you like fighting games DoA is the one to get.