What about the queue for the Gotthard Tunnel? I've been through it many times - admittedly never in the heat of summer because that would mean I was going to Italy in the summer and I never do that - in both directions and never, ever, experienced a queue for cars.
All the trucks are taken off after Luzern southbound and around Bellinzona northbound so that they can be put back on the road (after paying the truck toll and inspection) spaced sufficiently apart. This is a safety measure, and I'm happy for it. Also, quite a few trucks divert onto the truck train. It is required that trucks are no closer to each other in the tunnel than 150 metres.
But, as I said, I've never seen a queue for cars into the tunnel. I suppose it might happen if they have to close a lane.
The tunnel is very straightforward. What I do is set my cruise control to 100kph (I think its 100) and just head through. There are areas that break-downs can stop in, and well as well marked and lit sanctuary areas.
The full length of the tunnel is fully ventilated, and covered by Swiss radio, and my Garmin satnav works in the tunnel.
The tunnel really is a non-event. It just needs a bit of concentration....
The Susten Pass is the one for the run into Interlaken if you want to miss the tunnel.
I don't know how you do with mountain driving so it is hard to say if one way or the other is faster for you. Of course, there is the Brunig Pass to negotiate after surfacing from the Gotthard Tunnel and turning left in the vicinity of Luzern.
The only time I run that pass was in mid June and there were snow banks at least 15 feet high in places, and a delightful lack of traffic in the rain.
I wouldn't want to try to persuade you one way or the other. Different people prefer different things.