It is very worth it to run T2 guardians over T1 guardians due to the price of materials, but yeah within the tier it's not much of a difference, and personally I just do the easy ones. Like in the Feiton group, I spammed the fire turtle or the ice bird, and never the tree or the super robot shit(which I didn't bother clearing until today with T3 gear, I just soloed them to get access to T3 guardians). In Rohendel group I just spam the turtle cause I can get it down in 5mins usually and that saves a lot of time. In the yorn levels I forgot what I did, I didn't stay there long on Scrapper though and on my Blade I'm just doing the first one cause I haven't touched her gear.
I'm also skipping guardians on bard/paladin until I'm full rested, cause they waste too much time. If I get Bard to T2 though I'll do them cause the mats prices are crazy(on EUC the T2 leapstones are 90-100g each, so each guardian kill is like 400-500g), but T1 is just a waste of time and I have too many things to do.
Apparently I'm reading they buffed the hp of guardians in our version which is why they take so long. Fucking stupid changes that would have made sense if they were doing a staggered tier launch so people didn't farm the guardians too easily and had "content" to do every day, but with our T3 unlocked shit, it makes no sense for guardians to take longer.