Felixflyer,
The main difference between Parts 61 and 141 is the standardization of training. Part 61 requirements are described in the FARs and can be accomplished by any instructor with category and class rating required. Part 141 is more regulated in that the student is required train and perform maneuvers, knowledge, etc according to standards in various stages of the program. The student will also accomplish stage checks enroute to the eventual checkride.
This also means that the instructor must be Part 141 certified by the program chief, or his designee, which helps to ensure a standardization of training in the program. The jist of all this is that as a student, you can expect a level of training standards that might not be received through Part 61 training.
If you are going to pay bucks for training, I would recommend a Part 141 program as there is more assurance that you get what you are paying for.
Good luck,
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