I use a mid-upper range one. It's good enough for teaching Android, but not enough for full time work.
SSD and a fast modem are a must. Second, I'd recommend at least 8GB RAM. It'll give you 5-10 min build times, which is a pain for debugging, but at least you can build layouts and write code without it freezing.
HP Pavilion is my pick. Keyboard and touchpad is a little janky. But the backlight helps a lot at night and it's gives the best power per dollar.