Most of that energy is saved for lifting heavy weights and going beyond failure. So for me a little stretch before workout and then a 15-20 min cardio.

I always hit cardio after I lift.

Most of the time I feel like I'm running on empty when I step on the treadmill which is a good thing, your body will start burning your reserve fuel aka fat to get you through the cardio. but also remember that to much cardio combined with a Low BF% will induce your body to start dropping muscle .

I wish I knew at what bf% your body will start to drop muscle to accommodate for the increased cardio, its different for all people unfortunately.

I've always stuck with after when i tried before it effects my lifting seems like im burned out

It depends on your goals. For someone endurance cardio based, like I was for a time or so (20-30K+ 2-3 times a week) it doesn't matter when you do it IF... Your primary goal is to last longer in your chosen field ie triathlons. Whether you smash out 5-20k run before your workout or after doesn't matter because you're getting the main tasks done anyway, everything else is secondary. It's like hitting the flat bench for chest day, it's your core primary exercise so you want to be hitting it first and with the most energy, focus and commitment. Specifity is key. You want a bigger bench you hit bench first with adequate cardio thrown in throughout the week. If your goal is to get big and strong then most of your effort will be put into your strength programming, or bodybuilding etc.

The secret I find is not when you do your cardio but how much and why. A 5k at a steady to moderate pace without challenging intervals, inclines and pace changes etc will suffice most people in keeping things in check for the added capacity in the gym to lift heavy and get bigger and stronger. But 10-15,20k+ and you're stepping out of building general fitness and conditioning and forcing your body to adapt to a completely different stimulus and one which is more for your runners, sports specific, swimmers etc.

If you're hitting the treadmill before a workout and you're a strength athlete or a bodybuilder you don't want to be making cardio your primary exercise. Same with after lifting weights you again don't want to be making the cardio you do afterwards primary. If it becomes primary you will start to see diminishing returns.

That being said, keep it simple. Before or after doesn't matter. It's what you are doing and why. You should know why you're doing certain things in the gym, including cardio. You want to know the difference between aerobic and anaerobic exercise and the benefits of both. Are you looking to burn fat? Just elevate your HR? Train your aerobic system, or your anaerobic system? What HRZ are you aiming for? Ideally you want to be in HRZ1 or 2 for cardio if you're looking to keep a general level of fitness, along with maybe a session or two of sprints, box jumps, rowing, air bike at HRZ4-5 to raise your anaerobic capacity without burning you out. Former can be done for 30 minutes, and the latter should only need to be done for about a few minutes to 10 at the most depending on the exercise you're doing and the time it takes to start hitting your anaeorbic system.

I do both my workout and cardio in the morning. 10 minutes warmup cardio on tredmill, then workout, then 35 minutes cardio on stairclimber.

Sure, I dont doubt splitting them up would be better from a metabolism perspective, but I am not looking good for money, so efficiency is #1.

Plus, putting them both in the morning gives me a better probability of actually completing them rather than having a long tough day at work followed by cardio and workout

The best cardio for me is a walk in a fast rhythm for at least an hour.

Fasted or Post workout for multiple reasons..
1. Because that’s when your blood glucose is going to be lowest so you’re actually burning fat vs just burning off the glucose circulating in your body.

and 2, Killing cardio before you lift is only going to leave less energy for your lift.. plus less effective bc of reason 1. (assuming you eat 30-60mins before you lift)

Afterworkout 20-30 minutes
Elliptical or incline at 9 or more on treadmill
If you want less cardio EAT LESS

For me I like a faster cardio in the morning.
the only reason it is fasted is because wifey makes my breakfast while I'm doing it. Real time saver.
I lift in the evening after work.

I think it's a matter of what works best for you. Everyone is different, so what's best for one person may not be as effective for another.

Pre cardio shake*, no breakfast before and early in the morning give me the best results. I never did cardio before or after a workout but if you haven't the time in the morning I'd do it always after the regular workout, except after leg day.

*
Green Tea
Caffeine
Taurine
BCAA
Glutamine

Post workout, first thing in the morning, or last thing before going to sleep have worked best for me. But honestly I’m so fucking spend after working out that I prefer to separate it from my weight session. I also think the metabolic spike from exercise is greater when you separate it into two sessions rather than weights and cardio all at once.