Both will bolt up to the 2JZGTE, but the R154 is a beefier transmission and can handle more power. If you're only looking at going 400-450whp, the W58 would work, providing you're not gunning it off every traffic light.
As for the ecu, I'm no expert, but I think you can use the auto ecu for a manual, but not the other way around. There may be some additional wiring issues, but nothing too serious I don't think.

 

I have done lots of reading and research and it really boils down to this.

If you already have a w58: baby it and hope it doesn't grenade, eventually it wil

If you are auto: why waste time and money on a w58 swap? do it right the 1st time with r154, not that much more expensive. Especially with Blizzy's research and amazing finds on the oem soarer parts to convert the MkIII supra trans to fit in an SC300.

 

I reached 185mph and I crapped out. It was still climbing..
Very stable, and yes it can pass 190 if you have the right gearing.

 

I tought the w58 was bolt on and the r154 needed somes mods (extend the linkage) i dont really know i read thread but the were about swaps that have been done in an auto supra... more details would be good

 

ya you have to extend linage.