m in Israel: “Are those the only 2 items on your budget, so one is at the expense of the other? These are two mitzvos, and everyone should try to give as much matanos leevyonim as they can, and to fulfill the mitzva of mishloach manos in the best way they can.”
You have a point. The basis for what I wrote is based on the fact that generaly Matanois L’evyoinim is done on the quiet – the only guy who knows what you gave is the shliach, whereas Mishloach Manos everyone sees what you are delivering, making it more tempting to do be more generous in Mishloach Manos.
The Oznayim Latorah says a similar idea regarding donations to moisdos. People generally donate more willingly towards buildings, where a plaque with their name is displayed, as opposed to day-to-day running costs, where no-one will know about the donation!