Answer is neither because everything is subjective, and everyone reacts to different compounds in different ways.
Set and setting is obviously important as is dose.
Personally I would choose shrooms over LSD as I prefer organic sources.
Obviously 5g's is not going to be mellow ;-) were 1-2g might well be, but not if you're at a rave vs sitting at home with close trusted friends.
Whatever you do, do not smoke weed with either as some folks find it relaxing, but other finds it incredibly anxiety and stress inducing.