These are the things I looked at when I purchased my cot.
- Overall stability as a 2yo can really swing on things, especially from the outside trying to climb in to visit his brother.
- The way the sides drop down. Some have 2 metal clips where as others have no clips at all and you drop the side by leaning on it and pulling up. Personally I thought this was easier as it is a one handed operation when you get used to it.
- Adjustable height as it's easier on your back if you don't have to bend down too far with a newborn.
- Castors, though I think most have them.
- Plastic capping to prevent damage from chewing.
- The overall look of the cot can affect the price if it is a chunky design.

Another thing I might add is that my particular cot has to be dismantled if it is to be moved out of the room. I don't know if that will be an issue for you but seeing as I've moved several times now it's a pain, and is something I wish I'd had to consider at the time I bought it.