I also prefer one a day. I like the feeling where I can say “I’ve finished.” I’m also more for them being a little shorter (like the 10 for 10 scenario) because on the big scale, it will let people who may not have as well developed troops a better chance to finish them a little quicker and not feel as frustrated by the process, and on the personal scale, grinding out matches to complete things that I would never normally use isn’t that much fun. Sure I can ignore them and treat it like the PC version of the game and do what I would normally do, except as I mentioned at the start, I like being able to say I finished all of them.
Of course you could do a hybrid thing, where you have some “easier” tasks that could be for that 10 for 10 and then say save the 20 for 20 for other slots to try and appeal to both kinds of players. And alternatives to the gems could be glory as mentioned, or even an Event Key (which I know, 15 gems, but still fits within the talks of rewards).
Another possibility would be to create another tier. Talk was having the tasks scale for 150 and below and then change for 150 and up. Well, I know there is quite a different motivation for players who may be around 200 and those who are over 500. This way you can have the tasks aimed for the 1-150 crowd, another for 150-499, and a 3rd for 500+. And while I would suspect that the 500+ are the 1%ers of the game, it would still give those players a little something special or more challenging to do.
Edit: Since I see you responded. While 3 glory may be the baseline for 1 PvP match now, this too is something that will change with the next update. So you could get as little as 1 Glory based on the time of PvP match you choose, all the way up to 9 Glory. I’m guessing these future changes are also being taken into consideration as far as planning the Task Economy.