Step 1: Analyze carbocation stability.
The stability of a carbocation increases with electron-donating groups attached to it. The \( \text{CH}_3 - \text{OCH}_3^+ \) carbocation is stabilized by the electron-donating \( \text{OCH}_3 \) group.
Step 2: Conclusion.
The most stable carbocation is \( \text{CH}_3 - \text{OCH}_3^+ \).
Final Answer:
\[
\boxed{\text{CH}_3 - \text{OCH}_3^+}
\]