If you're asking which international airport to fly into from England to visit Ubon Ratchathani, then it's Bangkok's Suvarhabhumi International. From BKK, you could either fly via domestic budget airlines or take a VIP bus or the train to Ubon Ratchathani. Ubon Rathca is a pretty large town with lots of amenities and is close to the 'emerald triangle' where Thailand, Laos, and Cambodia meet (and not too far from central Vietnam).
I just read that the Khmer ruins of Preah Vihear wihch the Thai call Khao Phravihan is soon to reopen following nearly a year's dispute between Cambodia and Thailand as to the border eventhough it was determined several decades ago that Preah Vihear belonged to Cambodia as part of their Khmer empire/heritage a milleneum ago. Anyways, Preah Vihear is best accessed from the Thai side and it's a great excursion from Ubon. You can take a bus to Khantharalat which is the nearest town to the border. It could be a daytrip from Ubon, returning in the evening without any problems transport wise.
If you want to visit Laos, you're several hours away and there is even an 'international bus' that runs between Ubon Ratcha and the city of Pakse in Laos. Pakse is a large city but is a junction tranport point for destinations in southern Laos such as the 4,000 islands, Wat Phu in Chamapasak (another Khmer temple and UNESCO heritage site) or the Lao Bolaven Plateau which is 'coffe country'. Lots of great waterfalls to visit in this area during the rainy season. Anyways, have a great trip!
After two weeks of travelling we took the nighttrain from Ubon Ratchathani back to Bangkok. We booked a first class sleeper, the prices aren't hight, 1,246 Baht for the trip, ... so around 25 euro... we were looking forward to the trip as we already had taken the nighttrain from Bangkok to Surin before. But this time we weren't lucky, the door to our 'room' was closed... and this was a sign, after it was opened we found that our sleeping place contained many cockroaches, the whole waggon contained these bugs.... yuck, we didn't sleep for 12 hours and arrived in Bangkok very very tired..... but still the train is a good and cheap option to travel around...
When you arrive at the Ubon train station, many tuk tuk drivers will try to hustle you. I would decline those pitches and walk toward the station. You will find less assertive drivers that will give you a better price. This fellow charged 60 baht to get from the train station to the Laithong Hotel. However, we tipped him 40 baht because he drove safely, was nice and obviously needed the money.
By bus : there?re both ordinary and air con bus from the Northern&northeastern bus terminal (Mochit) daily. For more details call : 936-2841-48 ext 601-606 (ordinary,air con,VIP)
Other private public bus company :
Nakornchai tour 02936-0244
Cherdchai tour 02836-0199, 936-0253, 936-0611
By car : From Bangkok ,take a route No. 1 (Phahol yothin) to Saraburi Province then turn to route No.2 (Mittraparp) and continue to No. 4 (Chokchai-Dej udom) to Ubonratchathani. Or the route Bangkok- Nakornrachasima and continue to No.226 pass Burirum, Surin , Srisaket and end at Ubonrachathani
If u want take bus from BKK to Ubon its takes 1 day but by airplane its takes only 1 hour... UYou can ask taxi from city to Airport, not expensive...