Teebo only removes TM when he has stealth, so the question is which keeps him in stealth more often. He gets 2/5 attacks from stealth with his special, but his leader ability grants him a 55% chance every turn, however his special becomes a bit bugged. When he is leader his special only guarantees one turn stealthed instead of the stated two. But when he doesn't have stealth but you really need his TM reduction you can still use his special and gain the one turn stealthed. After that one turn it then reverts to a 55% chance to be stealthed. The TM he gives to the whole party is just icing on the cake.
If you are in a guild doing any raiding up to teir 5 I would recommend getting Teebo up to 5*. That's only 145 shards, or about 15 days of GW. Then gear him up to have 30% or 40% potency. Reaching 30% is relatively easy, however that extra 10% makes a huge difference in how often his TM gets resisted.