Personally, I'd really like to see a movie where Ran isn't helpless and uses her karate. xD
To be honest, a few of the movies would have done better as specials or filler arcs. I think an interesting movie would be centered around a case that Conan solved in an earlier movie. With new evidence, an escaped or unidentifiable culprit, or new rash of serial murders in the style of an old foe could prove to be a difficult case. I prefer when the production company doesn't try to involve as many side characters as possible, and would like to see another case where either Conan knows who it is and has to find the evidence, or has to suspect friends and allies. It would be interesting to see a case where a drug similar to apotoxin in chemical structure but successful in its murderous application was used, or where the organization was not involved in Conan's case or trying to find him, but became an obstacle in the investigation. Personally I'm tired of bombing movies and supposed twists where they obviously (to me) arrest or suspect the wrong person, and would like to see one involving Conan investigating a high-stakes case without being dragged into it due to coincidence or Agasa/Kogoro/Detective Boys' involvement in one aspect of the crime. Also, one based in Beika like the originals would be great.