It depends on what your goals are too. Are you looking to lose weight or tone up the the weight you have.
Resistance training ie weights burn tonnes more calories than most cardio. Like they said above, find activities you like. Listen to music or audiobooks as you do it. But definitely make at least half your gym time on weights. Pushups, crunches, medium weights with high reps is what you want. You want to get sweating and breathless and use all your energy before you leave. Calorie deficit will make your body start reaching into your stored energy locations to survive while building your muscles gradually to replace.