It is a bit like asking why you have a favourite colour. You will know what it is, but explaining why is another matter. There is also a world of difference between the oriental nationalities - personally, I don't find Chinese girls particularly attractive compared to Thais, and Chinese service levels are also generally much poorer.
I think a lot depends on what you want out of your punt. To some, the girl's looks is all important - this will be a matter of personal taste. I find most Brazilian SPs seem to be absolute stunners, for example, but unfortunately I am after more than just looks.
Personally, I go more for the overall "experience". I suspect it is no coincidence that my two top nationalities, Thais and Hungarians, both tend to be accomplished masseuses - I quite enjoy a massage either to relax into the event and/or to wind down after. I recognise that some punters, however, will just consider this a waste of time and money.
Oriental girls, and Thais in particular, seem oriented around looking after their man, and are extra attentive to your needs. They will usually help you undress, help you wash and dry (and if you are lucky, even join you in the shower for a raunchy assisted shower), and likewise help you wash and dress after the event, even giving you a token gift on your way out. They have a lightness of touch that can be very sensual, but equally are prepared to take deep throat or a hard pounding in their stride. Can't recall a Thai SP who wasn't prepared to snog me like I was their long-lost boyfriend (unlike Chinese, many of whom seem very reluctant to DFK). Nothing is too much trouble for them, they will do what you want, when you want - sometimes they seem almost intuitive to your needs.
In the London area in particular, they are also remarkable value for money. When most London agencies are now generally charging upward of £300 ph plus £50-100 in extras for most girls, the asian agencies are generally charging £150ph all-in and with a discount for repeat clients. In my experience, it is very rare for a Thai SP, agency or indie, to charge extra for anything - even for anal. Unlike the typical Rom or Brazilian, where almost everything "iz xtra, baby".
On the down-side, oriental girls being quite subservient is great if you want to be in charge, but less so if you want the girl to take charge of you (in which case, you are probably better with a Brazilian, if you can find one who offers a decent service). Their constantly calling you "dahling" and such-like can also get a bit wearing after awhile.
The above is of course a gross generalisation - I have had some dud experiences with Thais. Like everything, there are good and bad. But my success rate with Thais has been far higher than with just about every other nationality. But, as I said above, it will depend on what you want out of your punt.
