I'd do a mix of both, maybe 85% long, 15% short. Personally, I would make the short grass in the form of shooting lanes. The deer will bed in the tall stuff and when they are beginning to feed for the night they will start off and stretch and do a little feeding in the short stuff. Heck, you could go one step further and turn areasof the short grass into small food plots. Then youu'll have plenty of cover for them to bed and in and food nearby, best of both worlds. I have a buddy who does this and it is amazing how these deer just appear from no where at his food plots.