Which punctuation mark dominates?
Using the question-mark alone is the formal, grammatically correct thing to do.
Informally, however, the use of ?! or !? is actually an interrobang, and you could write it with a single punctuation mark if you really wanted to:
What did you do to my sausages‽
I've never seen anyone do this before, though. Let me know how it works out.
I was going to just comment the (IMHO incorrect) answer and leave it at that. But that would mean there's nowhere for anyone to upvote what I consider to be the correct answer...
Grammatically-correct doesn't come into it. There's no rule of grammar that says just because a statement has characteristics typical of questions (in this case, starts with the word "What"), it must be terminated with a question mark.
In order to convey surprise/anger/whatever, it's essential to include the exclamation mark. So if you accept the basic principle that only one should be used, the exclamation mark should be kept and the question mark discarded.
In standard English, replace “?!” with the exclamation point.
Incorrect: What did you do to my sausages?!
Correct: What did you do to my sausages!
The website, WhiteSmoke, provides a good explanation regarding the use of exclamation point:
The exclamation point (!) is a terminal punctuation mark in English and is usually used at the end of a sentence with no extra period. It can turn a simple indicative or declarative sentence into a strong command or reflect an emotional outburst. It can also indicate rhetorical questions. Do not use an exclamation point in texts that are neither literary dialog nor personal expressive writing. It is inappropriate to put an exclamation point in formal pieces of writing such as a business resume, school book report, or a due college paper, as the style expected in these should be objective, standard, and informative. Using an exclamation point in such settings creates an impression of unwarranted exaggeration, which in turn is perceived as amateurish, marketing oriented or just plainly childish. Do use it in stories and personal communication, and even then, sparingly.