The differences are:
1) bezel color - executives have a silver bezel and the tacticals are black.
2) factory programming - tacticals are programed with a strobe function from the factory, executives are not. Both models can be re-programmed to be identical.
3) button type - executives have a flush button allowing them to tail stand while tacticals have a raised button for easier activation.
If you want a combination of any of these, like I did, you can order a light directly from HDS how you want it.
As for the 170 vs 200...that's probably the toughest decision. If money isn't a deciding factor, the 200 is probably the best way to go, IMO. I own a 200 but not the 170. IIRC, the 170 slightly outthrows the 200 because of the different emitter and tighter hotspot. With that being said, the 200 does very well.
Bottom line, you can't go wrong with either light. And if you find you don't like the button type or bezel color, they can be ordered separately and changed down the road. I ordered both buttons with mine so I could try each one and have a spare.