Any of those would obviously work, however Triumph is demanding 15/50 synthetic.
I called the Triumph customer service today and they said any 15/50 synthetic will do. Mobile 1 has such an oil and is readily available.
You can always order Motul 300V its a good oil. The post above by the goat whisperer is for the 2.3 liter in which 10w40 was set as a alternative. I think if I was going to deviate I would use a 20W50 like red line.
My dealer explained it this way. The piston rings are so large that their ability to maintain proper tension is reduced so the thicker oil is very important. They use the Motul but the sound of the engine changed a bit. I seem to hear more mechanical noise now, going to try and get the Castrol
My dealer insisted on 10W40 (Castrol fully synthetic), however I am not happy with the noises from the engine. It sounds clicky / tappety and generally rattley. Gonna print that Triumph notice and wave it at him.