On the subject of which one is better designed? Well... they are 2 completely different animals. When Weber launched gen1 SSP in 1990, they pulled all the stops by incorporating SS table top, heavy duty frame parts, and propane assist start system that is used to the current models. As I have mentioned, SSP frames are designed to withstand load just as is. On other hand, on gen 2 , all major parts are designed to be part of the frame structure. That includes bolted table top, secured rack, and the front and back panels.
IMO, design award goes to SSP, then gen2 with SS front panel and blacked out frame, gen4 with metal table, and finally gen3.
To me, both are completely different. I choose to keep em all.