It's Star Wars, i.e. objectively speaking all of them could be considered either great or awful depending on who is watching & which movie it is. Star Wars is like that, i.e. it appeals to people in different ways. Personally speaking I believe Empire Strikes back is overrated (i.e. the movie most considered the best in the series). Its opening is strong, as is the confrontation between Vader & Luke, but the rest? I don't like it. I didn't like the romance between Solo & Leia, the excessive wisecracking & C-3PO becoming one of the most annoying comedic side characters in cinema history long before Jar Jar.
I enjoy Episode III most, if I had to choose. It has so many cathartic moments, i.e. for example Anakin slicing Mace Windu's forearm off, followed by Windu's screaming & the "unlimited powerrrrr!" from Palpatine is like literally my favorite Star Wars moment ever (best cinema experience as well). The build up to the big moment is just so good. And the part of the duel on Mustafar when Anakin & Obi Wan swing on the ropes of the collapsed structure, Obi Wan lands, Anakin runs, backflips onto the small platform & casually twirls his lightsaber. That whole sequence is so awesome (best music as well).