it depends
traditional closed cell foam are light, cheap and robust, the denser the foam the warmer. downside is they are not that comfortable and don't pack down small.
Modern air mats are comfortable and pack smaller, but heavy, more expensive and you need a punture kit.
Serious Outdoors types use a short mat, it's only really your upper body that needs the comfort and insulation. You can usually fashion some comfort/insulation for your legs/feet. If you want the air mat and you just intend to use it in the spring/summer, then get one of the lightest weight ones they usually have in their ranges.