I have some experience with Thai and Air India but not Asiana.
Thai is great if you're on their new 787's ex Aus, though our eastern states friends may or may not be getting the fully lay-flat beds on all flights yet. Warning with Thai is that they can be somewhat unreliable with flight schedule changes when booking a long way out. But I definitely use them regardless, PER seems to suffer from less schedule changes but with less favourable onward connections.
Air India for me was hit and miss. Good hard product for those who like to sleep with legs akimbo. Entertainment content sufficient for one return Europe trip. Food interesting. One flight had the best service I've ever experienced and the next flight was on par with the worst ever. DEL airport is not my favourite, and the transfer desk was mayhem. We got through ok in the end, AI wouldn't accept our previously issued boarding passes on Singapore paper so we needed new ones, though this was communicated only by a furrowed brow and pointing towards the transfer desk. It took an extremely long time with lots of staff shouting at each other in ?hindi and not telling us if there was a problem with us or with the thousand other things they were dealing with at the same time. I would fly with them again, but probably prefer Thai.
