what do i believe

Unless you input your age, height, and weight into the machine at the gym, it's really just a random number based on the "average" person's caloric expendature. You could either take the average of the two, or just play it safe and go with the lower number.

If you feel more comfortable with the gym equipment's reading, go with that. I don't think MFP can be one hundred percent accurate because they don't know your intensity level during the workout. It's an estimate - in other words, when I put 45 minutes in on my spin bike, I have to be as accurate as possible about speed and even then I risk being a little off.

Invest in a HRM if you're really concerned about this issue. I do not have one (yet) but I've heard they are far more accurate than either MFP OR any piece of exercise equipment.

Regardless of which method is the most accurate, I would say each has a fairly accurate estimate, even if it's not perfect. If you put the work in, don't stress too much about it. At least that's my mentality. I like knowing how many calories I burn, but I base almost everything on how I feel - if I focus on a length of time or certain burn, I may not work as hard compared to focusing on my breathing, my muscles, my heart, and my overall improvement day to day. I lost 95 pounds first go around, and that is how I did it - not necessarily counting calories burned during exercise, but giving my all to the workout and letting myself truly improve and become stronger each and every time.

Definitely not saying tracking calories burned isn't important, though! I do that every day (along with food!). I'm just saying pick your poison, so to speak. Whichever method feels most comfortable is the best one for you.