When choosing new baseboards consider the finish. Whether it will be painted, stained, or left natural determines the material selection. Wood is the traditional choice, but it's not your only option. If you're planning to paint the trim, manufactured materials such as medium-density fiberboard (MDF) and plastic moldings (including urethanes and other synthetics) are good-looking, budget-conscious alternatives.
To save money when staining, select wood based on the appearance of the grain, and stain to personal preferences. Cherry, for example, is an expensive wood, but you can get a comparable look by buying birch and applying a cherry stain. The grain and hardness of cherry and birch are very similar.
About 45 minutes total (not including drying time) to sand, finish, and fill holes on an 8-foot length
Sandpaper (fine and medium grits), sanding block, tack cloth, putty knife, paintbrush, lint-free cloths, disposable foam brushes, #0000 steel wool
Using sandpaper and a paintbrush
Fill knotholes, sand
Baseboard, wood filler, mineral spirits or paint thinner, paint, stain, clear polyurethane or varnish
Protect the floor and wall with painter's tape before painting. Apply paint to the wood surface with short light strokes across the wood grain, laying down paint in both directions. Finish with longer strokes in one direction only -- working with the wood grain. Use only the tips of the bristles to smooth out the paint.