I meant better as in much simpler to learn and to write, more focused on the relevant subject, and the language's syntax changes very little over time.
As far as having unpredictable results goes all I can say is that every language does the unexpected, whether it's a bug or just behavioural. For instance I've spent several days trying to figure out a fix for why a PHP function won't work in the documented way, but will work in a similar (undocumented) way which makes it totally unuseable to me - maybe it's a bug, maybe not, the point is that no language is infallible.
Since we are (or at least I am) talking about 'better' as far as being an IRC scripting language then speed is of little importance. Can it do things a lot faster than I could manually? Hell yeah. It's fast enough then, at least as far as I'm concerned. It really doesn't matter how many hundred or thousand times faster Python or PHP is if all the script is doing is looping through a couple of dozen nicknames or channels and performing some simple command each iteration.
Simplicity is mIRC scripting's real strength though. It takes a few days of learning to be able to produce useful and meaningful results, the things which people point out as weaknesses (no OO, no data types etc.) are what allow that to happen. If you came to mIRC from a programming background then that simplicity may not help you, it may even make things worse, but the fact is that most people aren't coders - at least not when they first learn mIRC scripting.
Documentation is another plus-point in mIRC's favour. Other languages might have more content relating to them on the web, but it's widely distributed and much of it is deprecated or poorly written. mIRC scripting is one of the few languages where documentation is instantly available in one single file on your computer from the get-go. And obviously since anyone using mIRC will be on IRC, I think it's fair to say that mIRC scripting has the edge on IRC help channels aswell.
Of course for some jobs speed really is important, quoted strings, arrays, objects etc. are very useful, and as CloCkWeRX has pointed out all those things are accessible if and when they're required. My gripe is the apparent attitude that a few people have in regards to mIRC that mIRC scripting is just a hurdle to be jumped over in order to get to 'the good languages' via DLLs and COM objects. If Khaled went to the trouble of making a language don't you think it's worth a little bit of the user's time to see if that can do the required job more easily before looking to other languages?
Anyway, I'm not trying to get into a computer language pissing contest, I'm just saying that the the most important choice when coding is to pick the right language for the job, and when it comes to IRC mIRC scripting is often the right one.