Its a tough one as they are all of a pretty similar level and have all reviewed pretty similar as well, its hard as well when your a bit giddy from all the newness and hype of the latest film but I expect I would end up with:
1. Deadpool
2. Deadpool & Wolverine
3. Deadpool 2
The first was such a miracle it even came into existence but it was mad following it from the leaked test footage but it was such a relief it came out and blew away the horrific memory of Origins and how dirty they did the character in that. Its a fairly simple revenge story but with loads of heart in it.
D&W has just so many crowd pleasing moments and things people have waited 20+ years just to see in live action it will stick in the mind for some longer than the others, even if its plot is little more convoluted than the other two films, it rips into the MCU in more ways than one.
DP2 had some great moments and maintained the franchises levels from the first, Cable and Domino were great additions and it had some of its own nice surprises, the plot with the kid dragged down the third act a bit though for me, still a fun watch though especially the Super cut.