Every tourist that visits Bangkok will be suggested a visit at the Chatuchak nmarket, which, with the exotic animal trade, the bizarre cacophony of sounds, and the mix of smells and heat, matches the impression of a vast third-world bazaar.
MBK, on the other hand, in the heart of central Bangkok (very near SIAM skytrain station) is very first-world, with everything a Western shopper would dream of (BUT IN THAI PRICES). MBK has eight air-conditioned levels, each expanding in a pretty vast space, with hundreds of shops at each level.
You can find numerous banks and money-changing outlets, restaurants to cater to every palate and budget, from the usual Western culprits (McDonalds, etc.) to the truly exotic, and there are mobile phone and accessories shops (100s), videos, TVs, cameras, and other electronic equipment, clothing at bargain prices, souvenir and gift shops, countless cafeterias (including the usual Western Starbucks, etc.), and even massage centers to help you relax from shopping fatigue.