oh what to choose....
opt 1 gives diamonds for login in i guess, but then you'd get ppl just log in and do nothing (all i'm saying some might)
opt 2 gives it randomly for "doing stuff", so i guess that's better. make some quests that give diamonds and/or make it as a chance reward for being good little helper, and more ppl will do it
for opt 3 - isn't that kind of like opt 1, makes you log in often, but you may and may not get diamonds? with opt 1 you'd be sure to get them after, let's say 10 consecutive days or so (i wouldn't make it less then a week, that's for sure), and with opt 3 if you have such "luck" maybe never
a tough one lol
with my luck, i would say no to opt 3, but it has elements of free gifts daily so can't be that bad, so bring it on even if without diamonds
any one of them works, just give us a chance for them
as for amount, i'd say make it related to lvl of town hall, that might make ppl work on that goal