Ive got my A&P. I went to school for two years about 14 years ago and I havent touched an aircraft since.
My experience is that the problem with being an aircraft mechanic is that there just isnt (wasnt in my case) much call for it unless you are willing to relocate to a job. When I finished A&P school 14 years ago, I was in a position that I couldnt leave where I was and I made the decision to not commute 4 hours every day so I never did find an A&P job and have since given up on it.
Diesel mechanic. I drive trucks now so I have contact with a few mechanics. They are always greasy, they dont make ALOT (not bad wages but not A&P wages). they usually work fairly long hours, but as a diesel mechanic, you should never be out of a job. Thats something that cant be said about any job in aviation.
At this point, having the experiences I have, if I had to choose either diesel or A&P, I would go with diesel for the job security. 16 years ago, I had the same decision and went the other way because I heard about all the money A&Ps make and I found aviation interesting, but I never considered that in most of the country, you have to wait till someone retires or dies before theres a job opening.
EDIT: You know what, I changed my mind. If you want to work on aircraft, thats the one you should choose. The reason I didnt follow through with it is my fault and to this day I regret giving up on it. So, I will give this advice, do what you want to do and if you have trouble landing a job out of school, dont give up and dont settle for anything less.