My situation may be a little bit different than everyone elses, being Canadian.
A big factor for me was the money. The average salary for techs is minimum wage to $14/hr with no opportunity to advance.
I was very naive about the field of veterinary medicine. I did not want to be a vet because I thought that diagnosing and performing surgery was scary! I researched the responsibilites of a vet tech: prepping for surgery, assisting with surgery, dentals, placing catheters, intubating, monitoring patients after surgery, restraining patients, taking patient histories, cleaning, etc. and decided that I wouldn't mind doing that. A friend then encouraged me to begin volunteering at a clinic.
Before I began volunteering at a clinic, I volunteered at a shelter. I got to see what the shelter techs do on a day to day basis. I talked to the techs about their job. Their job is very rewarding, but seeing animals and tough shape and making next to nothing had taken its toll on them.
Then I began volunteering at the clinic. I got to see techs at work and vets at work. The techs have a very hands-on roll in the clinic and seem to keep it running smoothly. I also saw the vets at work. I started job-shadowing them and watching surgeries. I realized that surgeries were not as bad as I thought they were.. and they were actually kind of cool! I also got to see what went on in the exam room... you have this little creature in pain and you have to try to figure out what the problem is and what the best way to go about fixing it is.
I was very very undecided. I talked to friends, family, vets, and techs. They all encouraged me to try to get into to vet school first, then think about becoming a tech if that didn't pan out.
I had to do testing and an interview for the vet tech program because it was very competative. I got a tour of the teaching clinic, which was AWESOME, and I got accepted. It was very hard for me to decline. I knew I would have enjoyed the program and I would have been happy with my job, even though the pay would be kind of low.
Now I'm in debt up to my ears. I feel like I'm too far in debt to shell out $20 000 for tech school and come out only making ~$12 an hour. Expensive, eh? Graduates of this program have no problem finding jobs because it is so hands on.
I should mention that techs just don't work in clinics... they can work with small animals, large animals, work at zoos, shelters, work with pharmacutical companies, etc, at least here that is!
Bottom line... volunteer! Ask questions! It's very hands-on, fast-paced, rewarding, and so darn cool!
I know I rambled on there for a little bit, but I hope it helps!