I've been researching that very question the last few weeks at bobistheoilguy.com. Lots of very knowledgeable folks on that board. The short answer...it depends. It depends on what your objectives are. The primary advantage of synthetic oils is extended oil change intervals.
Numerous used oil analyses show that wear metals are similar between synthetic and convential oils. But synthetics can usually go two to three times longer than convential oils between changes. Fuel mileage increases with synthetics are minimal, if even measurable.
Which oil to use depends on your objectives. Are you trying to minimize costs? Go dino and change every 3-4k miles. Are you trying to minimize the number of oil changes? Go synthetic and have your used oil analyzed to determine how far you can go based on your unique driving patterns.
As far as which brands are best, the consensus at the oil forum for convential oils (in no particular order): Chevron/Havoline (same oil, different bottle), Pennzoil, Castrol GTX, and Motorcraft.
Synthetic oils: Mobil 1. Not all synthetics are created equal. Base oils are defined by their properties, and classified as Group I, II, III, IV, or V. Group I is the worst, Group V the best. Mobil 1 is a Group IV oil. All the other over-the-counter synthetics are Group III (Castrol, Valvoline, Pennzoil, Quacker State, etc.) The only oils containing Group V are specialty oils such as Amsoil, Red Line, Royal Purple, etc.
The high mileage oils usually have a very good additive package, which helps reduce wear. They also usually have a seal-swell additive to help reduce oil leaks. They cost more than convential oils though, and don't last any longer than convential oils. Castrol GTX HM and Pennzoil HM are two of the better brands.