There are two common styles of BCDs, wrap-around and wing. These can be used in both warm and cold waters.
The sizing of a BCD is the most important part, if it is too small, it may prevent you from achieving correct buoyancy. If one is too big, the BCD will move around and affect your movement in the water.
Another factor that will affect your comfort is integrated weight systems. Many dive centres abroad have budget BCD's that will require the use of a weight belt, which are noticeable during your dive. The comfort provide by integrated pockets means that the weight is carried by the BCD rather than on your hips.
BCD's also come in travel styles, these are very light weight, minimalistic and streamlined, perfect for taking abroad.
Once all these bases are covered then you can think about other features such as; D-rings, knife attachments, usage with twinsets.