[Kirathis]

I have not gotten around to reading them yet but a lot of recommendations suggest the Joe Kelly run which is collected in Deadpool Classic volumes 1-5, the Cable & Deadpool (yup, for awhile Cable was the more popular/well known character) series and the new series that started in 2013. Classic volume 1 also collects his first appearance and the first two mini-series.

Be advised though that the original Deadpool minis did not have the comedy aspect of the current Deadpool. That came around with Joe Kelly's run and has grown since then.