This question has been cleared up recently with very well substantiated research. Cardio and resistance training do not mix well. Whenever possible cardio and resistance training should be separated by several hours to maximize improvements for each type of workout. A simple internet search or search on ACE, ACSM, etc. will give you the answers.
I am asked this question a lot, and it really depends on client goals and when they are at their best for various training purposes. For general purposes, I would say put the energy first towards the goal of the day. If weight training is tops on the list for the day, then do that first and then cardio after. Energy will be best expended that way.
You will get many different opinions on this, so go with what you feel is best for the client that day.
I am a huge proponent of mixing things ups
There are many schools of thoughts on which one burns the most calories. Some say when you do cardio first, you burn your quick energy stores, putting you into “fat burning” mode during your strength section.
I prefer cardio first, this ensures that my muscles are ready for strength work.
I also like splitting it up in 10 minute sections/cardio/weights/ etc
Keep you body guessing!