Bangkok... A major cosmopolitan city of 11 Million people covering a vast geographical area. Temperatures are hot & sticky. You notice it immediately when you arrive at the airport. Like LA, likes of smog and air pollutants. The center of the Asian Stock Market. If you like New York City,
you'll like Bangkok. Plenty of great food and shopping. Inexpensive overall. Inland with no nearby beaches. However, a river runs thru it... Can you say "Boat Rides"!
In a few Words...
Phuket... A major tourist destination. Located at the southern tip of Thailand (1:20 Flight time), a mountainous peninsula, with a large sandy beach on the western side. One of the more expensive cities in Thailand due to it's huge tourist base. This is a favorite of family, couples, romantic getaways.
Pattaya... A beachside city just 90 miles southeast of Bangkok, easily accessible by Bus/Taxi/Limo (less than $30). The city has a population of over 2 million and everything Thailand has to offer. Temperature is slightly cooler than Bangkok and most days when it rains, it's short term. Common dress is beach attire, shorts and sandals.
Plenty of great food and shopping. Very inexpensive. Message Parlors & 7 Eleven's on every block.
Chiang Mai... Located 435 miles North of Bangkok (1:15 flight time) the city is located in a mountainous region where the temperatures are substantially cooler. Not a seaside tourist area but it made it into the 2012 list of "25 Best Destinations in the World. No Snow but it does rain with the higher elevation.