You can tell by the looks which gen they
are. The "F" series has a 4.5 inch barrel,
where all the later versions are 4 inch.
The 2nd gen is about the same as the current
VE version, except that I seem to remember that
one having no rail for lights, etc.
The current VE version has the 4 inch barrel,
and has the proprietary rail for lights, etc.
With the rebate, you can buy a new one for under
$300 in most cases. IE: the going local rate
the last time I looked was about $329-$339 new.
With the $50 rebate, that would put you a bit
under $300. I'm not sure if the warranty covers
only the original purchaser, or covers all
future owners. Might be something to consider,
and look into.
I think I'd just as soon get a new one if the
difference in price was low.
The "F" is probably the best actual shooter, but
I'd be wary of the frame crack issues with that
line. I bet more of an issue with the .40 vs
the 9mm..
The Sigma was originally designed for .40 S&W
though. Pretty sure anyway..