I would say a Arcane Spike. XXXL trap from engineer also works well, and a Jungle Forest spam/Druid of the Forest for cleanup, but with ceramic popping power for breaking the ceramic shell. A Sentry Paragon works too, but possibly unreliable. Ultra Jug for cleanup may work too. A Alcemist and Village buffed Sun Avatar works, possibly with Overclock/Ultraboost. Glue Gunner (4-0-2 or 5-0-2) with a
2-2-0 or a 3-2-0 village for EVEN MORE ATTACK SPEED (and Camo detection). I haven’t done testing, and can’t until Friday. However, these are what I have used in the past.
I'd personally use a Perma-Spike (X-X-5 Spike Factory, preferable 0-2-5), buffed by an Alchemist (2+-X-X). It should take care of the DDTs, though you will need to be careful that the Perma-Spike doesn't end up soaking up too much damage from the other MOAB-Class bloons, especially on Round 98, as immediately after on round 99, there's a rush of fortified DDTs.
Usually your win condition should be enough to take them (e.g. perma x clock, inferno x clock, etc.). If not, you can't go wrong with a 3/0/1 Sun God with 4/0/0 Alchemist. As LuckyDoggie23 points out, Arcane Spike is good, too.
0/2/3 MOAB Glue is a must for 95 – the DDTs will run right through your defense otherwise. Other stall towers work, too (0/2/4 boomer being the main one), but nowhere near as effectively.
Unsure if this still works, but 0/4/0 Ace (Ground Zero) should 1-shot DDTs, and 2 should be able to take 95 and 99. Not sure on that so don't quote me on that.
Pre-emptive Strike is alright, but it's far too expensive to be worth it. It solos 95, but dies hard to 99.
Overall: Get a better strategy if you can't beat DDTs, in conjunction with support towers like 0/2/3 Glue.
For just the DDTS, the cheapest way I've found to defeat them is a 2-4-0 spike factory. One or two of those can easily defeat the DDT levels. Unfortunately, it's not that great for other stuff, but it's cheap to add if you already have ways of defeating 97, 98 and 100.
Most of my chimp wins either used 6 poplust druids + obyn + MIB (and that's a great combo for DDTs; usually I get avatar of wrath by round 90 and the rest of the game is a cakewalk), alchemist + Permaspike, or Comanche Commander plus MIB, and those all handle DDTs easily.
2-4-0 spike factory is also great for 100, it can pop the outer layer and the DDTs on long maps, given how fast the BAD is (about as fast as a pre-80 BFB). Not a good idea for the ZOMGs though, as there is a maximum possible damage per ability of 15000 (?) on blimps, so one 2-4-0 is pretty much useless for massive slower blimp rushes like 94, 96, 98.
Best counter in my opinion is to upgrade rush a bomb shooter to get Bloon Crush, yes its possible to get an expensive upgrade even on hard, i've done it multiple times. The Bloon Crush upgrade affects these MFs too, no matter how much or how fast they come, all MOAB-class type bloons (execpt B.A.D.s) will get stunned and basically froze in place as the bomb shooter (5-2-0) should be supported by a monkey village drums. With this, any towers around can do the work to damage the DDTs since they get stunned every half second, literally frozen in place. Of course, placement matters where the Bomb shooter should be place. I've gotten as far as round 147 all thanks to the Bloon Crush upgrade.