Really too many variables for me (at least) to be able to answer this. Are we talking about tube vs. solid state? Tube amps, in general, have their own character, depending on the tubes (power or preamp).
There are some reputed transparent preamps out there that you could couple with a power amp and perhaps get the best results.
It really is largely subjective (in my subjective opinion). I mean, I consider my G-K stuff to be pretty transparent, but it still has its own "character". I'd offer up my Eden WT-800, but it has a preamp tube.
For me, it's probably easier to think of brands which are the *least* transparent, such as SWR and Trace Elliot.
JMO, which is most likely wrong.