It sounds as though you want to prevent a player from modifying his or her own stats.
Can a person’s cheating affect other people’s games?
If not, there is no need to do anything and you are wasting your time even thinking about it.
To add to what L.Spiro said:
If your game gets popular, people will try to crack it, and eventually they will succeed. This is inevitable. And once one person has, the internet will see to it that their work is available to anyone playing your game. You can then waste time changing things, but there will be more of them than there are of you and someone will once again crack it.
Just make your game fun and let people play it however they want to.
i think i should stop thinking about about cheaters and hackers then
but what about the other part of the question? saving and loading data
2D or 3D? 3D it really shouldn't matter. 2D, aspect ratio. Design your assets for the highest resolution you support, its easy to downsample and the results are better than upsampling. It's aspect ratio that really kills you.
Then again in mobile its mostly a non factor, there isn't the huge variation you see in mobile. On a huge PC screen, letter boxing is more accepted for non standard resolutions, and they dont have the massive diversity ( like 16:9 of the Galaxy Note to the 4:3 of the iPad ) that you see in the mobile space. Graphics made for a 16:10 look fine on 16:9 for example. Graphics made for 16:10 on 4:3 look like crap.
it is going to be 2D.
you said "2D, aspect ratio" then you said " It's aspect ratio that really kills you.", but do you mean it is better to design with the highest resolution?
also check this image, i put the resolution 1920x1080 but it shows different resolution