Display and Processor
The Nokia X and Nokia X+ both have a 4 Inch WVGA display which is pretty usable on Nokia X but is quite soft on Nokia XL. The Nokia XL uses the same WVGA 480 x 800 pixel resolution on an inflated 5 Inch display. The Processor used in all three smartphones is same 1 GHz dual Core Snapdragon S4 but the RAM capacities backing up the processor differ among these smartphones. The Nokia X features 512 MB RAM where as Nokia X+ and XL will both feature 768 MB RAM. the added 256 MB will definitely boost performance.
Camera and Internal Storage
The Nokia X and Nokia X+ both feature a 3 MP camera at the rear for basic photography needs. The camera hardly qualifies as a decent shooter. Though MP count can be misleading while determining camera quality, but paltry pixels in Nokia X do affect its quality. The Nokia XL comes with a slightly better 5 MP camera unit and is also equipped with a front 2 MP shooter unlike its other two brethren. The Nokia XL will also feature LED Flash support at the back. The internal storage on all three devices is same 4 GB and can be further extended to 32 GB using MicroSD support.
Battery and OS
The battery capacity is 1500 mAh in Nokia X and Nokia X+ and this amounts to 10.5 hours of decent battery backup on both the devices. The Nokia XL has a 2000 mAh battery which augments the battery endurance to 13 hours of talk time on 3G.
Key Specs
Conclusion
The Nokia X and X+ are exactly same with respect to body design, dimensions look and feel. The only difference is extra 256 MB of RAM on X+. Nokia XL will offer you slightly better imaging hardware and bigger display size compared to Nokia X+ but the performance will be same for both the devices. If a 5 inch display and front camera ranks high on your priority list Nokia XL will suit you better.