Which would be bloodier Olympic or Coronet?
Probably Olympic. The Japanese were going to throw pretty much everything in the envelope at the Kyushu landings. The U.S. casualties in the period of D-1 to D+3 would likely have exceeded 100K, especially if the Kamikaze pilots managed to follow instructions hand ignore warships and strike at the transports & LST. Japanese losses would be around 100,000 KIA, possibly more, depending on how much of the militia actually turned out and how many civilians didn't get out of the landing zones before they started getting shelled.
Coronet is something of a mystery, not in the plans, but in what, if anything, the IJA would have left in the hopper. The U.S. was going to continue to pound the hell out of Honshu with heavy bombers while Olympic was taking place. The number of super heavy squadrons was going to more than double by the time Olympic was scheduled (the 8th AF was scheduled to start B-29 operations in early September out of Okinawa, a move that would have allowed for all of Honshu and Hokkaido, which had, until then, been outside of the range of Tinian based bombers, to be targeted. Just that change would have resulted in ever increasing material losses as previously "safe" supply locations would become vulnerable. The Japanese intended to expend nearly all the 10,000+ kamikaze in inventory against Olympic, as well as everything left of the surface fleet and all the surviving ocean going submarines. There would also be the near irresistible tendency to want to reinforce the Kyushu forces if they were doing better than expected.
A couple notes regarding some of the other posts -
The Japanese were well aware of how vulnerable their tunnels were vulnerable to flame thrower equipped tanks, heavy SP guns, and aircraft rockets. A considerable effort was made, starting with Saipan, to locate defensive positions where they were sheltered from these sorts of attack by terrain or through construction of dog-leg entrances. These efforts made it necessary to dig the defenders out the old fashioned way (probably best illustrated by the trouble the Shuri Line offered on Okinawa.
The Japanese battle plan was to extract maximum casualties. A critical part of this was the expectation that the U.S. would follow the same plan and absorb massive losses. That was unlikely. The U.S. intended to use nuclear weapons in a "tactical" role (at least six were earmarked just for the opening phase of Olympic), just the heat pulse of a weapon would be enough to literally roast defenders under cover and kill those above ground with both blast and debris, providing a 500-750 yard cleared zone. Most critically, had the Japanese begun to extract the sort of casualties they hoped for it is close to a given that Truman would have allowed the use of chemical weapons. Unlike the potential for use in the ETO, or even earlier in the Pacific War, the scenario during Downfall was very positive for use, primarily because the potential for Japanese reply in kind was, by late 1945, almost non-existent. The belief of the Japanese that the stronger they resisted the better the final terms would become is simply in error. What would have happened is that the U.S. would have done whatever was necessary to reduce American losses, the impact on the Japanese be damned.