Well digitally they are identical and upwardly patch compatible, So the only difference is between the DACs used. Personally I don’t put much into that, any character difference due to DACs doesn’t come anywhere near in comparison to the capabilities of a TI to be meaningful. Just having unique effects per channel Is very significant, the FX section on the TI is amazing and you can dedicate a channel just as an fx unit using the inputs.
I would like a B or C at some point though if I ever see a bargain, but they are overpriced I think these days with a TI not much more and given the choice the TI is a no brainer for the sheer scope of what it does. I would be surprised if you don’t absolutely love it, and doubt you will be wishing you got a B instead
The other difference is guaranteed polyphony on the B vs the TI, but in reality I don’t find that’s a problem in the way I use the TI.