Sean, I'll need to be brief before I get thrown off (the Web is in diabolical strife here at the moment). All very good advice above. Apart from protracted theory lessons there are some software solutions which will give answers that range from excellent to absurd, and you can tweak the parameters till the cows come home. At the end of the day the final decision requires your ear as judge. Send me a PM if you want more on the software - it is not that easy.

The other factor which influences my decisions about chords is the vocal harmonies. If I'm playing with other singers who have chosen a particular vocal harmony line, are happy with it and won't budge from that line, then the chords need to be shoe horned to fit the harmonies. Under those circumstances you can eitheruse your ear or you can examine the harmony note and whether it can be incorporated in your chosen chord. In my experience this occurs most easily with the choice between Major chords and the associated Relative Minor chord, that is D versus Bm.

Regards, John