Versus usually, but not always, refers to the debate between SW and ST. Covering such topics as: Which franchise has faster ships? Which franchise has better technology? Which side would win in an total war scenario?
The "versus" debate is widely considered to be settled. The ICS provided official quantifications of the capabilities of Star Wars warships that far exceed those of Star Trek vessels. Nonetheless, there are fanatics who insist that the ICS is not canon or is flawed.
Versus debating is not limited to only SW vs ST, but can be applied to any matching between any science fiction franchises, from fairly balanced matches, such as Firefly versus neo Battlestar Galactica to outrageously unfair matches, such as Star Trek versus the Xeelee.