1. Recommendation.
- I would recommend the 521. I feel with Nokia's excellent support and app portfolio, not to mention hardware, you will be best off with it.
2. Memory.
- Windows Phone sadly does not allow saving Apps to the SD card. However, one can utilize most of the system memory for SD by telling the phone to save all media (Music, Pictures, Videos, etc...) to the SD, essentially giving it roughly 7GB (after OS used space) for Apps. Which unless you are downloading a ton of high-end 200 - 400mb games, you shouldn't fill that up to terribly quick.
Also, the Ascend W1 only has 4GB memory (according to GSM arena) and only supports up to 32GB sd cards, while the 521 has 8GB memory and supports up to 64GB sd cards.
3. Pictures.
- I would say it takes decent pictures. Its no 920, but images seem to appear nice.
Here are some pictures for example of image quality:
http://forums.windowscentral.com/nokia-lumia-521/225708-521-user-pics-vids.html
http://forums.windowscentral.com/no...1st-pics-flickr-my-brand-new-lumia-521-a.html
As you see, the camera is fairly decent. (and raising or lowering the ISO can make the image clearer, or brighter)
4. Other:
- Granted, the Ascend W1 has a slightly faster processor, flash, compass (most likely), and ffc, however, WP8 is just as good with 1GHz processor as it is with 1.2GHz or 1.5GHz, and so on, so forth, and the flash and ffc are only necessary if you plan on a lot of video calling and night photography. The Nokia Lumia 521 will also have better support, being a Nokia device, as well as has better apps and more software features. Lumia Storage check allows you to clear temporary files, which is useful, and software such as Access Point make sure your network settings are correct. You get applications such as here drive, here maps, and others, as well as 4G and WiFi calling (latter to come in a future update on May 20th and requires a tmobile subscription, whether prepaid or main plan)
Overall:
If you are wanting the best of these two (or Memory is a must), go with the Lumia 521. It wins out almost all ways.
If you require either flash, a front facing camera, and/or (possibly) a compass/magnometer (which doesn't effect navigation, despite its name), you should go with the Ascend W1