In general I would say the further back the better. That is to say if you will have a good Gib (High level and attack speed) along with some stunning towers. This is so you can hold off the creeps from dying as long as possible to give as much time for Keys, Hidden Door, Muli & Balu to get there procs off as well as Mr. Iron ability time. Now that being said I had mine in the middle because I turned my Ganesha into Mr. Iron so he was max level. As I said I had a Muli as my primary main to covor for Mr. Iron to power up. Would have been better to use Muli as a CC card for more time but oh well. Also it is good to note that saving potions for as long as possible wouldn't hurt if you plan on using the rings. I did not use a single offensive potion until I had both rings. Tho I did use waters, I had over 170 Chance/Quality at by wave 50 lol.
Maybe I'm just getting some pretty crappy hands or something.. I keep getting like 4-5 pots by lvl 5 and they are always Atk Spd and Crit.. =/ I'm testing this out right now: 1,3- Huli (Replacement of Gib on 3 after Muli gets jacked on Bananas) 2- Witch (Huli Support) 4- Muli 5- Minatou 6- Pub? (Haven't decided 100% yet, Maybe another Gib?) 7,8,10, 11, 13, 14- Pub or witch 12- Bear Hunter (No idea of what to replace with) 15, 17- Witch (Support for Gib) 16- Gib I hope this test runs well. =D