I wanna buy a apple mac. but I am not sure which one is suitable for working.
Any advice will be appreciated.
Any modern Mac should work. Personally I buy refurbished ones from Apple's online store usually.
Check out macsales.com. Sometimes they have apple-refurbished macs with full AppleCare warranties for the same price as the Apple Store. However, they're tax-free. I bought my latest MacBook Pro from them and saved hundreds in sales tax. :)