I use a wild cherry...
...because I got all this
...on craigslist local for 45 bucks
Very mild sweet smoke which I've really enjoyed on my pork shoulders not bad on the chicken and I was suprised on how well I liked it on my beef ribs. Once I run out I'll probably pick up some oak. I use royal oak lump to start my fire in a chimney then straight cherry. So far I've enjoyed the results.
To be honest I cannot recall ever having smoked chicken so I have nothing to compare it against.