bro, anything that gets your ass sweating for more than 25 minutes is good..every summer i get cut without AS and all i did was do at least 20-30 minutes on the bike....i dont' go by all the technical shit of having your heart beat elevated at a certain degree for a certain time..you know when your burning fat. after first 5 minutes of warmup, pick up the pace and do the machine enough to make you start sweating by the first 10 minutes...my favorite has been the bike..just get a walkman, listen to music, and put your mind somewhere else..cause i hate cardio..but after a while got bored of bike..no just run..
Running is like the best cardio you can do, it burns the most calories..unless you want to go skiing