Nah for me First Class was the best hands down. Was a Charles and Eric origin story and was really well done.
Sure X2 was a better action flick, and DOFP a better sci-fi flick. But FC was everything that differentiates X-Men from others in the superhero franchise.
First two Deadpool movies were also fantastic. But obviously more comedic. But sure include Deadpool as X-Men movies. Given they all featured X-Men, which is basically the same as the first Three X-Men films.