Your levels 41s, train them at DexDorugreymons, or find a party at Oil 3 until they're 46.
Your level 53, train it at Dark tower, and if it can one skill kill Gizus, then go to Gizus. Dark tower is recommended for their cracked eggs which are 250b each (Which equals to 25m per stack of 100). Good for money.
Your level 31, just find a party at Oil 3.
Parties help you a lot when everyone's grinding of course~