"Storehorse" -- strong, lightweight, collapsible, less expensive than most competitors, nice handy platform serving as the horizontal spreader, sacrificial top, and no gee gaws. Without a doubt the best plastic sawhorse I've ever seen. They are available in several strengths, based on the number of aluminum tubes in the legs. The least strong has been more than sufficient for my every task, but we're I stacking sheetrock or parking my car atop them, I would opt for the stronger ones -- I have a mixture of strengths in my shop. Comes with a lightweight plastic top, replaceable with a sacrificial half 2x4 on edge that sits in a channel. A full 3-1/2" would require screwing the 2x into the channel.
Trojan legs -- super strong, very heavy, easy to configure and to store. Uses a 2"x4", x6", x8", or anything as desired for the top span of any length -- no tools or fasteners. I use them for custom sawhorse-based jigs. They are great, but harder to carry as legs or assembled due to their weight.