Huge difference bro.
Injectable is simply amazing, in my opinion. It's cheap, and I generally use it for appetite stimulation, immune system boost, and especially for diluting painful gear.
Every time I feel a cold coming on, I do 3 days at 1000mcg/day and I feel great!
B12 is water-soluble, so there's really no worries about taking too much because your body will just expel what it doesn't use.
Yeah, a lot of good bros think that it's just a placebo effect, but I really believe in the stuff, on the occasional night when I go out drinking, I come back and do 1000mcg, it boosts liver efficiency and I wake up feeling a lot less hung over than the nights I forget to take it...
Just my opinion...