The Speed Twin is ideal if you need a two up bike. I like the styling but find the Thruxton more appealing.
If purchasing today just for solo use, I would still go for the Thruxton R.
With the Thruxton R you get the better suspension and brakes. The main weight difference between the Speedtwin and Thruxton is in the wheels. The Thruxton R factory spoked alloy rims are about the nicest looking rims I've seen on a production bike, so I'll pay the weight price. The weight difference can be cut down quite a bit with the Outex tubeless kit.
The other reason to think about the Thruxton is the fairing. Its almost worth having the bike just so you can hang that fairing on it. The original 60s Thruxton had a nice fairing but the one designed for the Thruxton 1200 is exquisite. Whoever designed it really nailed it, every curve is as it should be and the fit to fuel tank is perfect.
It's also good to tuck in behind when up against strong headwinds.
I don't care for the Bobber styling.
There you go, some strong opinions based on my personal bias ( and 20,000 kms riding a Thrux R).
Glen