The diamond armory is a whole lot better than the regular items.
The best non-diamond items are as of now:
+138 atk, +69 def
216750 upkeep cost
Battelle Tail System;
+72 atk, +162 def
490908 upkeep cost
+145 atk, +114 def
554700 upkeep cost
Just getting rid of the upkeep cost is in many cases worth it (half a million for the Jag, while the Lotus is 0.)
But if you are in it for the long run, then I would suggest looking at getting mercs instead of items for diamonds. Having 2 Jags is so much better than just 1 lotus, if you can afford it.