The best results come from personal training because it is designed JUST FOR YOU!!
Period -- END OF STORY!!
Your personal training program is unique to you and your strengths, weaknesses and goals.
Do you enjoy group training and classes? Well GREAT!!
Tthen try adding some of those too as your cardio workout.
And look at it like that. If you add a few classes a week to your training as your cardio, you will find these group fitness classes to be a great little motivator. And a great calorie burner.
Just remember they do not replace strength training.
And for those who have special needs (such as hypertension, weak or tight muscles, osteoporosis, etc) group fitness and classes may NOT BE for you. You should seriously discuss ALL WORKOUT goals with your doctor. And be sure to mention to your doctor your desire to take group fitness classes as your doctor can determine if these are right for you and which ones to consider.
And remember that classes where they use weights are not strength training, they are cardio classes so don't get confused by group training. It can be a great addition to your workout but rarely is it the best solution as your only workout.
The number one class I recommend are the bicycle based classes such as spinning or Ride. Again, these are not for everyone so after you have the ok from your doctor, be sure to discuss your class plans with your trainer in order to ensure they are the best fit for you!