Share 'What's the best email marketing utility? Why?'

I need your recommendations. I'm currently in the market for new email marketing software. Through our corporate umbrella- we use a product called "Subscribe". It has its plusses and minuses, but it is very cost effective for our purposes. However, without going into all the details, it may be necessary for me to find a new program to use. Just a quick outline of our volume: We send approximat...