I'd go for both, really. You can find M7 at many TJ Maxx and Marshall's stores for about $20, and with the A*Men, you can get the 1.7oz bottle (the cool black rubber one) along with the shower gel and deodorant stick for like $45 online if you look around. There's no point in buying the big bottle of A*Men as it is so incredibly potent.
The M7 is excellent for the more hot and humid nights (at least in my opinion, I'm sure others will disagree), and is truly magic on rainy evenings. A*Men can get nasty in hot weather, so be sure to use sparingly. Also, when applying A*Men, spray it far away from your body- if you spray it onto a small area of your body, it will be too potent and a bit acrid. When you let it spread out, all of the notes will come out in all their glory.
Hope this helps...