BWG707 is correct, but I would also consider something more portable and "pocket size" for when you are at work or out in the town at night. For that I would recommend looking into either a 510 or a KR808D-1. Those two are the most recommended and purchased PV's. Lots of brands make those models so do not be confused if it does not say 510 or KR808, do some research and you will figure it out.
As for the more expensive PV's, I believe those are great for at home or for extended travel, mods usually have bigger batteries and can last for a while before charging but in exchange are bigger and not as easy to carry around when you are out of the house. I for one am going for a portable unit that I can carry comfortably in my pocket and then when I get used to it and want something better/bigger, i'm going to try out the GLV2 which has caught my attention.