KiteJan

The best is a specialist kite shop - you can get good advise, good after sales care, etc. but not everyone has a kite shop near them, or would feel confident going into one.

I would strongly recommend having a go with the expensive and/or powerful kites before buying - from my experience most flyers are only to happy talk about their kites & let you have a go.
I got my first (& second) kite from the French sports shop chain Decathlon. If starting out & don't know much about this then go for a relatively cheap kite - a Delta costs around £15 including lines and handles. Once you have got to grips with the basics & know how to fly the kite & are sure that you want to continue then it is worth spending more money, especially if you have had a go on the different types.

Although people who are into kite flying in a big way end up spending quite a lot of money on large kites it doesn't mean you can't have great fun with a small cheap kite. At the end of the day it is about having fun, not how big your kite is.