Killing more of a lesser con will yield more loong gold experience. DOWNTIME is the leveling killer. Minimize your downtime and you'll level faster.Monsters: It's very important to understand the monsters you're fighting. If you've never fought them before, obviously you might be surprised by some of their tactics. Some mobs nuke. A LOT. Others do a lot more damage than like conned mobs.Understanding the cons is extremely important as well. At low levels, the con range is easy. If you level after you receive the notification that you've gained a free level, you won't gain enough bonus experience for an entire level.
But the con range changes as you gain levels. Orange can be as high as three two levels above you, yellow can be as low as four levels below you in the higher levels.
By observing how the mobs change con as you level, you can decide which mobs are best for you to hunt in order to gain the most experience over time.