The 28-135 seem the best travelling lens amongst your 3 choice in terms of coverage but again it depends on your style.
I love street photography and can shamelessly shoot near to people subject and it is good for landscapes. So my 17-40 is always in my travel bag. I couple it with the good ól 50/1.8.
My another travel set up is the tamron 28-75 with my newly acquired sigma 15mm fisheye.
I never bring tele along for travel because I do not usually need tele. I only bring tele for revisits when I know which place require tele shoots.
Determine what are the subject you want to shoot in vietnam. Landscape? bring 17-40. Street shooting ? bring 28 - 135. In my opinion, 70 - 200 may not be necessary for travel use. The best is to bring both 17-40 & 28-135. But if you want to bring only one lens, choose 28-135. For me, I would bring 17-40 & couple with a 50mm.