I’ve seen all 3 and I actually liked all them. I found Bob and Carol the most interesting, but a lot people haven’t liked it. And so my second pick would be Soldier’s Play, which I thought was very good. I liked Grand Horizons too, but I found it more forgettable
My favorite was Bob & Carol. But I also really enjoyed Grand Horizons. I highly recommend Unknown Soldier. I'd avoid Soldier's Play since it was extremely dull, boring & poorly acted.