Are you new to reloading or just looking for a new powder?
My recommendation for newbies is to use Trail Boss. (BTW it is also a pretty clean powder) Because it is designed as a very bulky powder.
Unique is not the best powder for lighter charges in high volume cases, such as 38 special/357 since it is position sensitive within the case and can affect velocities/pressure quite a bit.
As for a clean powder, Titegroup is good, or if you want a faster and cleaner powder, then Clays. However you must be very careful with Clays, only suitable for lighter loads because it is so fast burning. Plus charge weights and volumes are tiny and double charges are really easy to miss.
W231 is a clean powder BUT ONLY if you load max/high pressure loads, and the same goes for many of the mid to slower pistol powders.