What oil to use is something that has been debated everywhere for years...If you were to stick with a name brand oil, i.e. Mobil, Havoline, Valvoline, etc. you should be fine. If you're looking to save even more money, some of the house brands are okay too - usually the parts counter people will be able to tell you who makes the house brand. For example, I believe that Mobil or one of the other big companies produces the generic brand oil sold at WalMart.
Switching from conventional to synthetic in an older, high mileage car should be done with caution. People will say that the synthetic will cause leaks, which is NOT true. The thing with synthetics is that if your engine has an oil leak and uses conventional oil, it will leak even more with synthetic simply because the properties of synthetic are such that it is in a simplified sense, "more slippery", which is one of the reasons why synthetic oil is far superior to conventional. If the engine doesn't have any major oil leaks, there isn't any reason not to switch, unless cost of the oil itself is an issue.
Which brand of synthetic to use is basically up to you. Honestly, you can't go wrong with any of the name brands here either, Mobil 1, AMSOil, Castrol Syntec, whatever. I'm partial to Mobil 1, but that's my preference.
Just make sure to stick with the weight/viscosity of oil recommended in your owners manual, and have the API certification on the bottle/box (usually on the back)...