utill vs till

They are both prepositions meaning “up to a specified point in time.” They are subordinating conjunctions of the equivalent meaning.

[i]I will play games until 4 p.m. - Preposition
We can talk till 4 p.m. - Preposition

Until you behave, I will not take you to the zoo. - Conjunction
I will not take you to the zoo till you behave. - Conjunction[/i]

I prefer until, especially as a subordinating conjunction.