In a reasonably big list eg 2250, which would you prefer? Or is it better to have both? I'm leaning towards the skinks as I only have to paint a few normal skinks chamo colours rather than pay $20-30 per terradon. Is there a reason to take both?
They both have a place in your list. However, I think the chameleon skinks are just a little bit better for the cost. They get an additional -1 to hit (on top of the -1 for being skirmishers). If you will be facing skaven (who should take the storm banner), you should go for the chameleons for sure. The storm banner will ground your terradons.