61 v. 141
A 14 CFR 141 flight school is an FAA-approved school. The FAA has approved the school's training syllabus and its facilities. When you train under Part 61, you need only an instructor and an airplane.
Quality of training varies under both systems. Both ways work. Both ways can take more, or less, time. A Part 141 program in theory requires fewer flight hours. You can earn a Commercial-Instrument in a minimum of 190 hours. Under Part 61, you need a minimum of 250 hours. The truth of the matter is most people go over times under both systems. There's no harm or foul in that, and it doesn't reflect on your abilities. Sometimes, flights go over times. Sometimes, there are part(s) of the program that people don't pick up right away. Even if you're progressing, you may need an extra flight(s) to hone your abilities to standards.
Many of the well-known 141 programs take people from zero time to their Commercial-Multi-Instrument in six months or less. They can do it because the only thing they do is train pilots. There's no reason why you can't finish in six months under Part 61, but a lot depends on where and how you obtain the training. Many FBOs offer Part 61 training, but some are more serious about it than others. You have to factor in numbers of aircraft, maintenance, instructor availability, and organization.
Hope that helps.