Where do you live, and how big are you willing to go?
If you can find one (they're more rare than a unicorn), the Nokia Lumia 1520 is a fantastic phone with really solid specs and great performance. You won't be disappointed with it, but the screen size is a little hard to, ah, swallow at first. It's the legendary Windows phone flagship, up there with the Lumia 920 and Lumia 1020, although I'd put it one step higher. It's over two years old yet it can still keep up, and you won't be lacking in features.
The Lumia 830 is a great phone as well, especially with the prices you can find it at. It's not super powerful (but it still runs really well), and it has a lot of neat, extra features like Glance Screen, microSD card support, Qi wireless charging, etcetera. If you can find that phone brand new within your price range (I also suggest looking around for some good deals) you're getting a great design, fantastic build quality, an amazing camera and a decent phone overall.
If you want to go a bit cheaper the Lumia 640 has the same screen and processor as the Lumia 830. You won't get Qi wireless charging and some of the extra features, and the Glance Screen isn't as advanced on the Lumia 640. You'd also be giving up the sleek, metal-framed design of the Lumia 830 and that impressive PureView camera. The Lumia 640 is a great phone for the price you can get it at, I would just weigh exactly how much you want to get out of your phone against how much you're willing to pay for it. The Lumia 830 is the better phone, but it costs at least twice as much. Do you want that more premium design, do you want that superior camera?
I own both the Lumia 830 and Lumia 640 and I could easily recommend both. The Lumia 640 XL might be a good choice too if you want a bigger phone.