This is a very personal choice that can differ from match to match. You need to take so many factors into consideration like sun, wind, shade, etc. The general rule is if you consider yourself a good starter or not, and whether you prefer to return or receive.
The advantage of serving first is that if you get broken early and your opponent holds, then you are only down 0-2. However, if your opponent holds then breaks you, he has a chance to consolidate that break by his serve.
On the flip side, some players like to return first to get themselves warmed up and get used to the court surroundings. In general, serve first if you are aggressive with your serve.