I have oak cabinets in my kitchen, they have been there since 1995. This was the year the house was built. I want to make them darker with a stain. I know I have to clean and sand, but my question really is about the stain itself. I want to make them look newer but is there a better stain that looks better on oak cabinets or is there a better option for want I want? I also want to replace the vinyl floor and paint the walls.

Dark cabinet will make the whole room look darker and dreary. And once you go darker there's no going back to a lighter color with out stripping back to bare wood.
For any stain to work it needs to be applyed to bare wood for a long lasting finish.
Clean the cabnets with orange cleaner ot TSP before any sanding takes place or you'll just be grinding in the oils and dirt.
Plan on at least two weeks of stripping cleaning, staining and sealing.

Its not the stain that matters, but the prep and the final top coat. Use the back of a door that you do not typcially use to test the color your planning to use. If it does not come out right you can always bleach it out and start over again.
As far as what stain to use. There are several types on the market today. Some with poly in the finish, single step application and those without multi step application. Personally I like the multi step method better. It allows you to re-stain the same board several times to get it darker if that is what your looking for.

My suggestion is to go to a quality type paint store, not the big box ones. They can assist you with the entire project. From selection to application.

If your also doing the floor and walls as well. I suggest that you get some samples of what your using when picking out the stain. Contrasting colors such as dark cabinets and light walls/floors oftetimes looks good. But its all about personal taste.

Remember also. The final look will depend on several factors. How big the rooms is. If its small light colors are better, Makes room look bigger. What type of hardware you have on the cabinets. Sometimes just changing this feature with more expensive handles knobs and hinges will change the entire look of the room.