The second one will be faster (technically). This is because mIRC will stop the comparison as soon as the first match is found, and skip to the action. An equivalent would be something like this:
if (x == 1) ;blah1
elseif (x == 2) ;blah2
elseif (x == 3) ;blah3
In this case, as soon as the first match is found and the associated action is taken, mIRC skips to the line directly after the last elseif (or else) in that if-statement.
Someone else can probably describe this better using colors and/or diagrams.
-genius_at_work
