I'd say that sm57
is a must have ... somehow you'll end up using one or two from time to time, so it's good to keep them around since they are not $300+ mics.
Basically Betas have more of a high presence than SM series. Maybe also some extended bass response as Heavy G mentioned. So if you're searching for a mild live vocal (less presence in the mix) Betas will take some knob twisting to get there. I personally like to get my sound from choosing the right mic for the right source, so last time i did a gig i ended up choosing an sm57
on vocals over beta58... beta was just too much in combination with a female "lots of sssss" type of vocal.
So now i know that i'll need a couple of different vocal mics for main, and i can manage with what i have left for backup vocals.
Haven't heard Heil mics yet, but i'm not that keen on thick vocals since i don't do much heavy stuff. Plus i almost always end up rolling some low end from vocal tracks as they just come through clear that way for me. Don't know, maybe it's the preamps in my mixer...
Just for the fun of it i will get an old SM58
(i know they're pretty much thesame with SM57
, but the grill makes a difference), and maybe buy a wind screen for SM57
, the A2WS (do you guy's even use windscreens indoors to mild it up a bit?). also the beta57 ... heard that on vocals and i want it. Maybe an Audix OM7 for some louder applications.