I like the luxury vinyl planks . . softer on feet and quieter too - the high end ones look like cerused wood finishes - they dieal with wavy floors a lot better than tile which will crack or require a ton of prep ..

Cost efficient would be with the vinyl plank. Look and feel of real wood without the hassle of up keep. But I would recommend your subfloor be properly delt with vs laying directly on a wavy floor for warranty purposes.

Google American Estates tile by Marazzi Tile. Very beautiful porcelain tile that mimics hand scraped wood. Rated for light commercial use, ideal for residential. 6 x 36 or 9 x 36 planks available. This would be a more expensive and permanent upgrade. Any unevenness in the subfloor can be corrected by using a little more thinset in that area. I will also recommend using a modified mortar with a latex additive (thinset) which will allow slight movement in the subfloor and not cause those pesky hairline cracks.