>>29844377ORAS was the worst. D/P has its speed issues and HM overuse but it's a generally better experience in terms of regional exploration due to its openness and the overall difficulty is a very welcome accompaniment to this.
Additionally, gen 4 was the first gen to attempt developing the characterizations of gym leaders as a whole via appearances outside gyms (and this is more glaringly notable when you compare it to ORAS where only Norman and Wattson really have any notable screentime outside their gyms); not a big deal, but always a nice touch when done right.
Another issue with ORAS is that it's based on Hoenn which while it has a better balance type-wise than shit like Sinnoh's 3 fire types could ever justify, a lot of Pokemon in Hoenn are so notably weaker than others around them that it just feels shit to use them. DP doesn't really have this issue.
DP has far worse swimming, but the lack of water routes doesn't really make it as bad as it could be. Hoenn by contrast still has far too much fucking water.