It's till (although you sometimes also see 'til).

"Till and until are generally interchangeable in both writing and speech, though as the first word in a sentence until is usually preferred: Until you get that paper written, don't even think about going to the movies. · Till is actually the older word, with until having been formed by the addition to it of the prefix un-, meaning "up to." In the 18th century the spelling 'till became fashionable, as if till were a shortened form of until. Although 'till is now nonstandard, 'til is sometimes used in this way and is considered acceptable, though it is etymologically incorrect."
- http://www.thefreedictionary.com/till

Till ist die ältere Form, dann gibt es noch until, til und til'. 'til ist relativ neu und viele Style Guides und Lexika sagen auch falsch.

Agree with #1.