Hi Brad and welcome to the forum.
It depends upon what type of game you're developing, if you mean your game to be similar to a turn based rpg, then it wil be the battle system itself that will provide the difficulty.
If your meaning this to be more of an arcade/action title, then you need to setup your action in such a way as to be interesting to play and require judgement from the part of the player, not merely a repeat of a bopit style, hear it, hit it type of gameplay which we've all seen before.
Either of the systems you mention could be employed in such a way, with the player having to judge a monster's position and guess its movement speed relative to their attacks I'd say, especially if there is a maze, and dungeon exploring element as well.
As to good game examples on Ios, while we've got hopes for sonar islands, sadly a lot of the better Ios titles like the somethinelse games have been demolished by the apple development monster.
Feer is absolutely worth a play, since while it is! a fast action, arcade avoid as much as possible game, its probably the single best iteration of such a game on the platform.
You might also have a look at tank battle endless gunner as well, which employs some interesting tilt mechanics and requires the player's judgement.
Hth.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)