The real answer, not the one you tell yourself when you're excited about the apartment.
The 30% rule uses gross income. Use your actual take-home pay — that's what hits your bank account, and that's what matters when rent is due.
Don't forget about next year. Will you be able to afford a rent increase? If you're already stretched thin, a 5% bump could push you over the edge.
That apartment 45 minutes out might save $200/month in rent but cost you $300 in gas and commute time. Do the full math before you commit.