Shortly after you've decided to get your pilot license (it's actually called a private pilot certificate, but we'll let you slide if you call it a license), you're going to start look at possible flight schools for your training. If you spend any amount of time digging into the flight school options, you'll quickly find out there are two different types of schools.  A part 141 and a part 61. 

These names refer to the section of the FAR/AIM or Federal Aviation Regulations/Aeronautical Information Manual which governs or regulates the school.  If you look at part 61 and part 141 you can learn everything there is to know about these regulations.

Let's break each one down so you can understand the difference.

The most attractive aspect of a Part 61 flight school is the flexibility it affords you as a student. You're not bound by a specific lesson plan which allows you to jump around a bit in your training. Of course, you're obviously going to have some limitations in how much you can do. For example, you're not going to be able to do your solo cross country before you do your solo flight. That goes without saying.

Part 61 flight schools MAY, but don't always, so don't assume, offer you a more affordable route to your private pilot certificate.  Because they've got few requirements put on them by the FAA they presumably have lower overhead costs.  Again, this isn't always the case, so don't assume. 

I completed my flight training at a Part 61 flight school and feel I got a VERY thorough and professional training experience.  Just because they're under less direction from the FAA, don't assume you're going to get substandard training.  If you've done your due diligence in researching a flight school, you'll find there are many Part 61 schools that meet your needs.

Part 141 flight schools have a lot of requirements and are given a great deal of direction from the FAA. If rigid structure and a clear outline of what you're doing each session is what you're looking for, this may be your best option. There are very structured lessons and several checkrides you'll have to go through before completing your flight training. If you're more of a free spirit, you may want to look at part 61. 

The first thing people will tell you about part 141 flight school is the decreased number of hours needed before you can take your checkride.  While a part 61 school requires a minimum of 40 hours, part 141 schools only require you to have 35 hours.  The truth is, the average time it takes to master your piloting skills going to be over 60 hours.  So, don't let this lower time requirement be the deciding factor for you.  There are plenty of students at a part 141 flight school who need over 70 hours of flight time before their checkride as well as plenty of part 61 students who need less.  It goes both ways.

The place where you may want to look at a part 141 school is when you go on to your advanced ratings.  This is where your decreased requirements may actually have a true cost savings for you.  For example, if you're getting your instrument rating at a part 61 flight school, you'll need to have logged 50 hours cross country as pilot in command (PIC).  That's not a requirement for a part 141 school.  That's a considerable cost savings for most students.

If you've got access to the GI Bill from your previous military service, you can use that for your advanced ratings IF you're using a part 141 school.  The GI Bill can't be used for your basic private pilot certificate.  It also can't be used at a part 61 school.  So, for someone in this specific situation, it would clearly be to your advantage to utilize a part 141 school.

More often, I'm seeing flight schools offering both a part 61 program and a part 141 program.  If they're certified by the FAA as a part 141 school, they can offer those students who choose it, a part 61 training program.

This can be the best of both worlds for many student pilots.  Take your basic PPL under their less rigid part 61 program and then when you go on to your advanced ratings, you can stick with the same CFI's and aircraft, but shift over to the flight schools part 141 program.

Bottomline, it's all a matter of what you think works best for you.  Don't think about the time because flying is flying is flying, regardless of whether you're with a CFI or not.  Don't be in a hurry to complete your flight training.  Enjoy every minute of the time you have in the plane and if it takes you over 100 hours to complete your training, that's great!  Learn all you can and train to be the best pilot in the sky.