640 or 640XL... You want the updated Snapdragon goodness of Sensor Core.
Find a cheap 830I replaced my broken 820 with a second hand one, in perfect state, for only 150€. Couldn't be hapier with it (especially the camera and battery)
If you have to choose between the 2 options you gave, take the 640XL, definitely.
I wouldn't handle the XL well, so I'd probably spring for an 830 if I had to get a replacement.
(although I've been held captive by this Blackberry I just got)
Although, considering the age of the device, parts shouldn't be too expensive.
But hey, this is your excuse to move to a different device.
Looks like glass & digitizer combo is as low as $40 on Amazon. So the disciplined part of me says just fix it.
Interestingly, I don't see the camera button on the side of the 640 / 640XL. Anyone else notice that?
Starting with Windows Phone 8.1, the camera button requirement was dropped for Windows Phone devices.
So lower end devices lack that button, starting with the 630 I believe, of the current x30 lineup, the Lumia 830 is the lowest end device with a camera button.
It's not too hard to replace the whole lcd/touch assembly on the 920. It takes a couple of torx screwdrivers, which you can cheaply as well - a T2, T4, and T5. If you're comfortable turning a few screws, it's not a bad repair to do. Just get the screwdrivers in advance, or you'll be frustrated waiting for them to show up. BTW - I could not find a T2 anywhere locally, so I just ordered a whole set from ebay.
I did the exact same thing about an hour ago, although on concrete. Phone still works, as long as I don't mind 1000 tiny shards slicing my fingers. Shopping right now for a replacement, but Microsoft has been awful about releasing flagships. I like the Icon, but I use the glance feature, and don't think it works on that particular model for some reason.
Just be really careful to buy an OFFICIAL screen. I tried to replace my 820 screen with an "100% oem!!" Screen of eBay, and after a reset or update it will stop working, because I can clearly tell it's not oem.