Which level difficulty are you playing right now (Easy, Normal, Epic, Legend, Mythic M1, M2, or M3)? A good rule of thumb is that it shouldn't take you more than 5 min to complete a map. If you're completing challenge maps faster than 5 min, you could try the next difficulty. If you move up in difficulty and If your toons start to die a lot, you will probably want to go back to an easier difficulty. Marching to floor 200 will be very beneficial for equipment drops but you also get perks for playing the more difficult levels. Risk vs reward.