the m50 will probably yeild the best battery life.
for performance in gaming the m40 is best, the intel graphics in the m50 is just not up to serious gaming these days. the a70 is about the same as the m50 cause it uses older graphics that although dedicated are likely on par with the integrated on the m50 simply because of their age.
judging speed is difficult really cause what are you wanting speed in. the P-m in the m40 and m50 is better at some things than others, while the p4 ht in the a70 also is better with some things than others. if you are gaming they are about equal, but in rendering the p4 is better by a small margin.
yes the battery life on the m40 is not super great but you have to factor in that it has a very powerful graphics card which uses more power than the solutions in either other machine. also if you are at university like me you wont be needing battery all the time, many schools now offer power plugs in classrooms for such things are laptops, and in the library it isnt hard to get one at my university either. also you can remember that in your room (assuming you live in the residences) you are going to have plugins.
also think about what you are going to do with the machine, is it going to be a laptop for workign only or are you wanting to watch movies and play games on it too. if you are wanting to game and do movies you are going to want a bigger screen than a 12 or 14inch... cause if it is your primary entertainment center in your room its gonna have to do some of everything, meaning a 15.4inch would be a better choice.
i would really recomend not getting a laptop in first year thinking you are going to do all your notes on it becuase simply put you wont. it is hard to type as fast as some profs talk and even if you are trying there are often diagrams that cant be easily or quickly drawn on a laptop. i do find havin a laptop useful, especially when you are typing reports between classes or even in the library doing research.... but dont count on taking it everywhere with you and using it all the time. a pen and paper is much more realistic for classes.
really you have options but the best bet for you is either an m40 or m50 in my opinion.... just think about the things you want and get the one best suited to your needs.
BTW.... what universities are you two heading to? major/minor?