Usually an AT4040 coupled with a Shure SM57. I am finding the AT4040, while absolute go-to mic for vocals, is not doing it for me on the amp these days, though... not sure why. Just not sounding "right".
I play better through an amp.
For me, after you get over the tone and the analog/digital yada yada thing, the question is, "How do you get your best performance?" No one wants to listen to realistic sounding bad playing. My clients want a good take, that sounds good and is well performed. So how do I get it?
I've found I get it through an amp. It's just that, no more. I have nothing against the fractal.
I like wearing boots with jeans more than wearing sneakers with jeans. I have nothing against sneakers. Just prefer boots.
Do I think the Fractal sounds 100% as good as an amp?
Not really, but it's so close it wouldn't matter if I played better through the Fractal; if so, I would have one.
A 57 has a very sharp rise in response above 2 kHz, which some people like, and some don't. Of course, the off axis response and resonances and other things work differently, and the 4040 has to be a bit farther away to avoid overloading.
In contrast, the Royer R-121 has a fairly flat curve up to around 10K, where it begins a gradual rolloff. So it tends to sound a bit more natural, and its proximity effect on the low end tends to enhance the bass. Also, a ribbon mic has a very fast transient response, so it reproduces the pick attack, etc., and the leading edge of the waveform very well.
Horses for courses, as always when it comes to choosing mics!
Shure SM57 all the way, if I had a choice. I have also had to rely on impulses since cranking an amp is not always an option for me. Even then, I choose ones using the SM57