512 RAM isn't bad for most purposes, its not going to work with some fancy apps (but they are few and far between) and its fancy 3D games that won't work.
I would recommend looking at the 620 (the 630 is more of a sidegrade to the 620), the 520 is bottom-of-the-bargain-bin, but its not what you're looking for.
The 1320 is a fine option if you could live with the size. I wouldn't be able to, but on paper, its a reasonably powerful mid-range device.
Android is often percieved as superior and WP bad. A misconception. But either one isn't for everyone, know that.
Also worth noting that some Samsung ATIV phones might be a good option. They're generally underrated in these parts, but they can potentially be found for a good price.