I totally agree with lances 1, 2, 9 and 13. My recommendations for the rest are below:
Lance 3: I recommend moving the Cyclops into it in place of the King Crab (though the King Crab would complement the others very well, there's no better place for the Cyclops).
Lance 4: The Highlander would be fine, or you could move a Crockett in there.
Lance 5: The Exterminator is completely out of place. It really belongs with your Command Lance as an extra 'mech, like you suggested. Pulling it and the Cylcops leaves a pair of Crocketts that would mesh really well with Lance 4. Either two 3-mech lances or a 6-mech demi-company would be quite frightening.
Lance 6: Swap the Guillotine for the Bombardier in Lance 10. The Guillotine goes to Lance 8.
Lance 7: A thing of beauty, leave it be...
Lance 8: The Flashman and Dragon belong together, as do the Catapult and Wyvern. Bring the Guillotine from Lance 6 into this lance, and find another 4/6/4 to go with them. The Flashman and Dragon go to Lance 11.
Lance 9: Good to go, as already mentioned.
Lance 10: Leave the Griffin, but pull in the Wolverine, Starslayer and Lynx. The Bombardier goes to Lance 6.
Lance 11: Keep the two Champions, and pull in the Flashman and Dragon from Lance 8. The Wolverine goes to Lance 10, and the Shadow Hawk to Lance 12.
Lance 12: Keep the Shadow Hawk. Bring in the other Shadow Hawk to replace the Starslayer. Then bring in the two Kintaros from Lance 10. More on the Firefly and Phoenix Hawk below.
Lance 13: Good to go, as already mentioned.
Lance 14: Swap out the Assassin for the Phoenix Hawk from Lance 12.
Lance 15: Swap out the Cicada for the Assassin from Lance 14. This way, the Sling has a battle buddy.
Lance 16: Swap out the Hermes for the Cicada from Lance 15. Now the whole lance moves 8/12.
Lance 17: Put the Hermes from Lance 16 in for the Lynx that was sent to Lance 10. This pairs up with the Hussar nicely.
Lance 18: Why wasn't this on your list of lances you're happy with? :)
Leftovers: The only holes left after the above moves are a 4/6/4 'mech in Lance 8, and a pair of 3/5/3s in Lances 4 and 5. And of course there's the "bonus" Exterminator.
Please let me know what you think...