So I have had my camera and nifty 50 for a few month now. I just got my cashback from Nikon, so that's the deposit on my next lens. I was convinced up until about a month ago that I was going to buy an 18-200mm because it was such an 'all-rounder'.

Fast forward to now and I am thinking that I might go the wide-angle zoom option. One thing I have noticed with the nifty 50 is that when taking photos of my kids around the house is that it's too long. I of course usually step backwards and we're all good, but sometimes I feel like I miss the shot, especially when I prefer candid photos. I would like to take more street/architecture photos and feel that a wide-angle lens would fit the bill.

So of course, the more I read, the more confused I am about which lens to buy.

There is a local shop that has a second hand Nikon 10-24mm for $650, what should I be asking and looking for when buying second hand? Some of the other lenses and bodies they have on their site seem a bit exxy for what they are.

I also saw on some threads here on AP that the Sigma 10-20mm is a good lens, however, I have seen that there are two different lenses one f3.5 and one f4-5.6 - which is better?

Realistically I have about $700 to spend.

Thanks in advance!