If you are buying casual or recreational axles, any 7000 series is a massive step up from stock hardware.  However, if you are a competitive speed skater who changes wheels constantly to adapt to different track conditions and rain, spending a little extra on verified 7075 grade aluminum axles is the best insurance against stripped heads and mechanical failures on race day!
 
Compatible with most frames, compatible across brands
 
Standard silver 7000 series axles $3/ea