What's the best way to travel to and from BKK - Hua Hin?

If you don't to take a taxi, there are pretty comfortable minibuses that leave from Victory Monument. They are used by Thais, very few foreigners seem to know about them, so they are far superior to cramped rip-off Khao San Road things. Depends how much luggage you have...6 large suitcases won't do but a reasonably sized bag or rucksack is OK. (Or you could pay for two or more seats) You get them in the small side street on the left (in front of the hospital) as you come out of the skytrain. It's been a year or so since I took one so I don't know what the exact fare is now....150B maybe. Tickets are bought from a guy sitting on the pavement and the approximate schedule is every hour, on the half hour.

A private taxi would probably cost about 2000B

There are buses too from the Southern Bus station. Don't take one with an orange stripe on it, it'll stop at every wee town en route and take ages.

There are trains to Hua Hin too but they are slower and less frequent.

just a quick question..I'm thinking of heading down to hua hin..with a public bus. How long would the trip take?

Depends on the public bus. As I said, steer clear of ones with orange stripes on them. A minibus takes about 3 hours so a bus would probably take a bit longer as they stop more often. Buses leave from the Southern bus terminal which is a bit more difficult to get to than Victory Monument as it isn't on the skytrain route. When you take a taxi there, don't ask for "southern bus terminal" or you'll likely get taken to Sathorn which isn't the same place at all! Say "sathanii sai tai mai" instead. Easiest would be to get your hotel to write it in Thai for you. Oh and beware of the taxi tout sharks if you come back via the Southern Bus station ...get onto the main road and hail a moving taxi...they will be far less reluctant to use their meters.