I have two Laptop, i can only keep one, which is it?
Portability is of no concern, battery life is of little concern.
1st unit is an m18x R2:
256 ssd, two 750 72000 rpm hybrid
3rd gen quad core i7-3610QM
2g gddr5 Nvidia GeForce GTX 660M
windows 7 ultimate
Dual layer BR Reader, dvd-+rw
Intel 2230 Wireless-N
2nd Unit is an M17 R3
-Intel Core 6th Generation i7-6820HK Processor
-32 GB DDR4 Dual Channel 2133Mhz (16GBx2)
-1TB M.2 PCIe Solid State Drive+1 TB 2.5-Inch SATA Hard Drive (7200 RPM)
-NVidia GeForce GTX 980M with 4gb
-17.3 inch FHD (1920 x 1080) IPS-Panel Anti-Glare 300-nits Display
-Windows 10 Pro
-Intel 8260 2x2 802.11ac 2.4/5GHz + Bluetooth 4.1
Wait--why can't you keep both units?
As a corollary--is the other unit for sale?
As an answer--I would choose the M17 R3. What will happen to the M18x R2?
Well I would like to suggest you to get M17 R3. Just click on http://www.techomag.com/alienware-m17xr3-a-gaming-laptop-that-shouldnt-be-missed/ take a look of this webpage and it will help you to decide which one is better.
Definitely the 17 r3 as that CPU can be overclocked. Combine that with a graphics amp and you will be set for a long time. Both the CPU and GPU in the 18x are well past their prime and have no upgrade path. If you need a bluray/dvd drive, buy an external one for cheap.