To the OP, the use of filters will depend solely on what YOU are trying to accomplish with your shots. Please please please don't lose sight of this and get frustrated with the filter/no filter debate.
As an example I'll explain why I used a filter or why I didn't in some of my shots.
1) Filter: Yes, Grad ND. Why: The dynamic range of this shot exceeded the camera's capabilities. Without the filter I would have had to choose between a dark forground and a properly exposed sky or a properly exposed forground and a blown out sky. I wanted both to best exemplify the scene as I saw it that morning, thus the use of the split ND.
2) Filter: No. Why: The reflection provided a line from top right to bottom left, which I used as part of the composition, if I had polarized the shot the reflection would have been eliminated, along with the line, and we'd be looking at a shot of a leaf in a mud bottom puddle.
3) Filter: No. Why: This is facing north with light coming from the west. The northern sky is typically the darkest part of the sky, and had I polarized the shot the sky would have been closer to black and would have looked unnatural. My intent was colour so a black sky was not something I wanted in this shot. Had my intentions been B&W I may have polarized the shot which would have killed the reflection on the water, blackened the sky and added additional focus to the little boat. Again this decision not to polarize was a creative decision.
4) Filter: Yes. Polarizer. Why: I wanted to knock down the glare on the water and allow the lilly pads to create a leading line into the scene, without it the pads blended too much into the glare of the water.
5) Filter: Yes. Solid ND. Why: To slow the exposure time which allowed me to create this shot. My intent was to create an image with contrast, both in terms of subject (static vs motion) and in terms of tone (B&W).
I think you get the idea. So when you ask what should I get, that really is up to you as your choice to use filters or not will be determined by your vision and creativity, and not necessarily by any sort of rule or rules.