@ Shams
The arcade is the best value. You can buy an HDD off eBay cheap and you get a memory card in the meantime. For me, I bought a premium and have enjoyed it. However, I know the 360s aren't the most reliable things on the market, and I would probably end up buying an arcade one if it went out on me. I have a 20gb HD and can swap it over to the arcade with NP.
The best price point is the arcade. You can upgrade to a bigger HD later. And buy new - the warranty alone is worth it.
PM me your LIVE gamer tag when you buy it!