Ill/Rad would have still been the king for AV/Giant Monster soloing just because of Lingering Radiation. HT's base recharge is twice as long. With Rad, if you have perma PA, you easily have perma Lingering (and probably double stacked at times), so the hard targets aren't going to be doing much regenerating at all.
Not to mention the fact they aren't going to be shooting at you most of the time either. If I have to kill one single thing, Ill/Rad is my controller of choice.
On the other hand, if I was going to try the RWZ challenge, Ill/Dark might be the better choice. Ill/Rad is actually not the best choice for that in my opinion. The pets get confused when confronted with so many targets, its hard to keep a lot of +5s continuously controlled with Illusion, regeneration debuffs are not as game-changing there.
One of my best Ill/Rad stories happened late one night when I saw a few players in Croatoa trying to get enough players to take down the Jack/Eochai pair. They spent twenty minutes trying, and when I got there they were deciding to give up because they knew they could get the badge anymore: the two had spent too much time fighting each other, so they would not be able to deal enough damage to get credit. I told the four of them to not worry, I would get the badge for them if they trusted me. I told them to start wailing on the two of them while I debuffed the pair and kept spamming heals on them to keep them alive. I let them attack both for about ten minutes, and then when I calculated they did enough damage and the counters had reset I told them they would be killing Eochai now, then started using LR. All of a sudden, their damage took him out in like a minute or two and bang: badge. Then I told them to focus on Jack next, and soon enough Jack went down, and they got the second badge.
The amazing thing about Ill/Rad was not just that it could take the two GMs down. It was that I had total control over the process. If I wanted them to stay alive, they stayed alive. When I decided it was time for them to go down, they went down. In the meantime, the GMs simply could not kill those players as long as I decided to keep them alive.
Now that's a controller.