there is a difference , co op is something like training but you getting weekly salary . for example , if you are doing 3 years of engineering technology , you will do a training or co op after every 2 semesters . the regular is just doing three years direct without any training.
A regular study visa does not allow you to work for a company within the curriculum stated by the school.
A study visa with a coop work permit allows the holder to work for a company within the study visa period. However, this will prolong the time before the graduation of the holder of the student visa. It is an additional requirement unless it is included in the curriculum.
As to the question of which is better, it depends on the reason why you got a study visa. If you want "secured" employment or to test out the working environment in Canada, the the coop work permit is for you. If you are only after graduating faster to get a PGWP, then the regular study visa is for you.