[davecom]

If I have two connections, which takes presidence, the wireless or the wired, or if I have them both on, will it pick and choose and maybe I'll get more throughput?

[Tuoder]

First of all, it is precedence. I can be an irritating spelling nazi sometimes, although I'm hardly perfect.

Second, in my experience on my MacBook, the wired connection take over when you plug in. Which is faster depends on a variety of factors, and in some cases there is no material difference between the two, but wired connections are generally faster than wireless ones. My wireless connection is operating at 54Mbps. My wired connection operates at 100Mbps. My internet connection is only 1.5Mbps in either case, so it usually doesn't make a difference. I am simplifying matters quite a bit, but that is generally the case.

[rjt1000]

Originally Posted by davecom 

If I have two connections, which takes presidence, the wireless or the wired, or if I have them both on, will it pick and choose and maybe I'll get more throughput?

Network preferences->Show: Network Port Configurations->Uncheck the ones you don't use and drag the ones you do into the order you want them to be tried

[Sherman Homan]

or if I have them both on, will it pick and choose and maybe I'll get more throughput?

More throughput to what? MAC bonding or aggregating is common in server environments, pretty much unusable on client machines, and unheard of with mixed media like an ethernet cable and a wireless point. What ever you were trying to connect to would need an identical configuration, all of which dies the second you go throguh your internet modem.
On the other hand, your computer can't pick and choose and you don't want it to! Your ethernet connection will have a different IP address than your wireless connection so if they switched, your current connection would be dropped.