Don't worry about whether you should be running, biking, or doing some other type of exercise. Just pick an aerobic exercise (or a set of exercises) that you enjoy the most, then be consistent about doing it. Consistency is the key. Forcing yourself to do something you do not enjoy simply because you think it may better prepare you for elk hunting will not result in the consistency you need. Personally, I do a wide range of exercises. In the Winter, I cross country ski, snowshoe, bike, and stairclimb. As the snow melts out of our local mountains, I put the skis and snowshoes away and start hiking up the steepest hills I can find. Sometimes I load my pack up with an excessive amount of water to add weight. I use water so if I get in a bind or my knees start hurting, I can simply pour it out to lighten the load.
Also, many folks make the mistake of pushing themselves hard day in and day out. This is a big mistake. You do not gain fitness by pushing yourself hard. You gain fitness by giving your body adequate rest after pushing yourself hard. Most folks would do much better if they pushed themselves harder 2-3 times per week, and worked out MUCH easier the other days. Make your efforts very hard or very easy, and avoid the middle ground. On the easy days, you want to keep your efforts short and with very low intensity - so low that you can almost breathe entirely thru your nose and can easily maintain a conversation while speaking in complete, uninterupted sentences.