What over-the-counter decongestant is preferred ?

Depends: Spray decongestants like afrin (oxymetazoline) are highly effective, but should only be taken for a max of 2-3 days in a row. Longer use can cause serious side effects. Oral decongestants like sudafed can also be highly effective, and are generally safe for longer periods of time. In all cases, it is important use them according to their directions and to consult your physician if you have other health probs.