All three are solid schools for engineering and if your son’s goal is to work as an engineer in industry, I would say the cheaper options accomplish that goal well, as long as they are an otherwise good fit. Engineering graduates from any of these schools are not going have much trouble finding solid employment. Both Clemson and Georgia Tech have outstanding and well established co-op programs. VT’s program is not quite as established, but as the main engineering school in Virginia, there’s going to be a lot of on-campus recruitment there as well.
Note that Clemson OOS tuition and estimated total cost of attendance is about $5k/year higher than Tech, so that partially offsets the scholarship they awarded him. Clemson and VT are probably both around $30k cheaper over 4 years. Coming to Tech may or may not be worth that $30k depending on what you and your son value.
All you have mentioned is rigor, and if the only reason you are hesitant on Tech is because you think it won’t allow time for social and other development outside of the classroom, that really shouldn’t be a concern. Tech students have lives, party, and get involved, while still doing well in school. It’s not a party school and Tech will be rigorous and have better prepared students, but the coursework itself is not going to be all that different. Your son is not going to be competing for a limited number of As and Bs. Tech professors are generally willing to hand out as many As and Bs as the students earn rather than saying that only x% can fall into each grade bucket.
That said, unless your son plans to get involved with research, which is really where Tech shines, I not sure Tech offers $30k more value for undergraduate engineering than Clemson and VT. However, if your son is interested in research, or strongly values what Georgia Tech’s student body and culture have to offer, or has aspirations to pursue a career investment banking or management consulting, then the cost premium for Georgia Tech may be worth it. $30k isn’t tiny, but it is small enough that I could see this going either way depending on what you both value. Would your son be willing (or have to) pay for the difference in cost? That may be a good metric to decide if it’s worth it to him.