You have received excellent advice on this thread. Primarily that experience and talented engineers working with high quality performers can make any gear sound good, whereas great engineers can't make a shitty singer sound any better. But by now, you must have figured out that you can't polish a turd.
There is no one "holy grail" vocal mic or channel. Some singers will prefer a particular mic. The first question how does the singer work the mic, and are they consistent & good about their technique? You may or may not the ability to fix their method.
Next: the mics they are used to using, is it dynamic or condenser? Which is more appropriate? Do they need sensitivity for soft source, or the ability to handle high SPL without distorting and string off-axis rejection for loud stage monitors? If you are dealing with a rock vocalist, it's probable that you'll need a dynamic mic. The serious Pop, R&B, and Country singers more often go the route of condensers before a rock vocalist can.
There are literally dozens of threads here on live vocal mics. Before you go asking for a "Holy Grail" mic, which ones has your artist used and liked? Shure SM58, Beta58, Beta 87, Beta 57, Sennheiser 409, 441, 835, 431, Audix OM3, OM5, OM7, Audio Technica 5300, Neumann KM104, KM105, AKG 535EB, Telefunken M80, Beyer M69, M88, E/V 767.... the list goes on, and on, and on.
I have no less than TEN vocal mics I keep in my inventory when working with a new artist, but I usually have one minute to try two and then use the one I prefer, and that's what we get. If your singers is professional & experienced, they have a mic they prefer, and you should spend the time getting to know what they like about it.
After you have the mic you like and THEY like, you have to make a choice about path. I find it difficult to leave the preamp onstage unless your monitor engineer is in tune with your preferences.
The vocal path can be far and wide, a huge departure from the vocal mic. Ask your artist what recording of their voice they like the best, and find out what the engineer did. I have used, from time to time, everything from a Manley DVC to VoxBox to SSL Alpha Channel to the older Focusrite Blue Range vocal master to the Chandler TG2 to Daking 52270B pre/EQ to Avalon 737 to... well, quite a few more. I've never found only ONE solution for more than one voice. Sometimes I need a Distressor, sometimes a Neve EQ, sometimes the API, sometimes an SSL compressor to do gentle vocal comp/rounding adds the bit of glue. Being a knowledgeable engineer with decades of both live and studio experience makes a huge difference.
This may not seem very helpful, as you seem to be wanting an "answer", but the real answer is, it all depends- on everything.
Best regards.
JvB