The Falken Azenis RT-615 gives better grip on dry pavement than the Kumho Ecsta MX. For a side-by-side autocross comparison test, read this.The MX gives somewhat better grip in rain than the RT-615. Neither is all that great in rain, but the MX is not as bad as the RT-615.
The MX lasts somewhat longer than the RT-615, although neither lasts all that long; typical treadlife is 15-20K miles for the MX, vs 10-12K for the RT-615.
So it all depends on what you're looking for, and what you're willing to trade off. If you care ONLY about dry traction, then get the RT-615. Or, even better, get the Dunlop Direzza Sport Z1 Star Spec, if they make it in your size; it's even stickier than the RT-615. If you also care about wet traction and/or treadlife and you're willing to trade off some dry grip, the MX might be a good choice for you; there are also tires that are even better in rain and last longer, if you're willing to trade off a bit more dry grip than the MX.