Well since DMC4 is not available yet I will answer for only the 1st 3 of them. Although I do believe that in some things DMC4 surpasses the others. Anyway:
Best enemies? Devil May Cry. They were demonic, powerful and nice looking. Devil May Cry 2 enemies tried to be like the usual alien/devils in appearance and they were weak and ugly to boot. Devil May Cry 3 enemies were nicely done, but they seem incomplete to me (regarding the appearance). Also most of the hard ones were hard because they were annoying and not because they were cool.
Best weapons? Devil May Cry. Alastor/Force Edge/Sparda/Yamato/Ifrit and the usual range of guns. What else can I ask for. In this case I think it surpasses Devil May Cry 4, although it is too soon to tell. Devil May Cry 2 had the worst. Just the same sword moves with a different lump of steel. Devil May Cry 3 had some of my favorite Devil May Cry weapons (Yamato, summoned swords, Rebellion) but it had some pretty not cool weapons like Artemis and the rest.
Best characters beside Dante? Devil May Cry 3. Hands down. Vergil is my favorite villain and Lady my favorite female character. Devil May Cry had Nelo Angelo and Trish, but Nelo was mute and Trish a bit stupid (blonde

) so not for me. Devil May Cry 2 did not have characters beside Dante that I like. Except if you count Trish again.
Best music? Devil May Cry. The music in some places fills you with anxiety and horror as to not know what to expect next. And Nelo Angelo's music in the 3rd time you fight him (both in the cut-scene and in the actual fight ) rules. Plus Sparda's theme in the opening and when you make the sword is my favorite Devil May Cry music. Devil May Cry 3 music was cool as well. It has from nice quiet sogs to really fast to go along with you beating the bad guys but it had some useless ones as well. For example I did not like even one boss music except some of Vergil's fights. Devil May Cry 2 had some nice songs but still can't compare.
Best lines? Devil May Cry 3. All Devil May Crys have Dante saying the coolest things but Devil May Cry 3 has Vergil as a bonus to double the cool things that can be said.
Best moves? Devil May Cry 3. The style invention was the best thing that happened to Dante. Devil May Cry 2 had a great side-move while pressing 'O' and was really useful along with some other moves but Devil May Cry 3 had way more than that. Devil May Cry had the less moves which are on all Devil May Crys anyway so it can't compare.
Best attire & personality for Dante? In here I guess Devil May Cry 4 would easily win but oh well. Devil May Cry attire is my favourite. Even in Devil May Cry 3 I use it. Dante's personality is the best in Devil May Cry as well, even though the game is the oldest and the one doing the voice acting could do a better job, but still I like how easy-going but serious at the same time he is supposed to be. Plus he seems to like reading books and stuff since you can speak to almost anything in Devil May Cry.
Best environments? Devil May Cry once again. Although 4 would probably win in this too. It has gothic like castles and creepy demonic places. Although I prefer the demonic places of Devil May Cry 3, I did not like the inside of Temme-ni-gru at all. I preferred some of Devil May Cry 2's places from the tower to tell you the truth. But still I love castles and cathedrals so Devil May Cry 1 wins.
PS: Nice thread
