I haven't played with any versions of the Speed, but of the others, the Radical Pro is the "softest", IMO.
I can echo DonDiego comments on the BLX 6.1 95 16x18 and the Head Extreme Pro 2.0. Those racquets aren't nearly as different as the specs might suggest. The XP2.0 does not feel any stiffer than the 6.1 95 despite the ratings. I actually preferred the XP2.0 in that regard. Both are excellent racquets though.
Everyone has their own likes and dislikes, but I liked the BLX 6.1 95 better than the the Radical or the Prestige.
And, the prices is down to $164 now, so that's a plus.