The only “DSP” modes I would use are 1. Dolby Surround and 2. DTS NeuralX.
Otherwise, I would use “Straight”.
If you want better Dialogue, boost the Center Speaker Channel Levels by 3 or 4 dB or more if you have to (depends on movie, room, speakers, etc. Don’t be afraid to play around with the Center speaker levels. The salient purpose of the Center speaker is Dialogue, so do what it takes to make it sound good.
If you use the Android or iOS AV Controller remote app, you can also adjust the Dialogue level.