I'd choose the MX-3 before the MX-4 and I'll tell you why.

Matt / PA is as schooled in bow tuning, mechanics etc as much as anybody I know, he'll tell you that even he could not get the MX-4's to shoot properly to be satisfied with them. In his opinion ( and respected) they are junk. The MX-3's are fantastic.

So between the two you asked about, Spitfires.

And I agree with MeanV, if you want a solid 4 blade head, Slicktricks are your choice.