HTC One with unlimited data, easily. The One Max literally has the same exact hardware as the One, except it has a bigger screen.

HTC One.

The only thing that concerns me is the lack of expandable storage on the One and the screen size :/ .

Screen isn't an issue, trust me, you'll be now. Now, expandable storage on the other hand, I can see why. If it's the 16GB model, you should be fine. If it's the 32GB model, you'll definitely be fine.

I have little tiny kid hands. My Nexus 5 was to big for me when i got it :D (I got used to it. I was using an Iphone before. I didn't bougth it. Don't kill me please) So i wouldn't be concerned about the size. No sd card migth be a dealbreaker depending on what you want to use your phine for. Only music? Fine. Games+ Music still fine. Lots of games+ music+ video files not fine.

I'm mostly planning on putting my music library on there with a few old PS2 and PSP games to emulate and maybe a few episodes of anime.

How many gbs would the HTC one have if you go for it?

I dunno if the HTC One would be able to run PS2 and PSP games smoothly...

I dunno, I've never tried emulating those types of games on my phone.

From what I've seen from others it should be fine in terms of running it but I believe the model I'd get would be the 32GB version so actually thinking about it the lack of SD card slot should be fine XD.

32g is fine. No need for an microsd card then.

My G2 has 32GB of storage. At most I have around 10GB left, but then again, I don't put many videos and no music on my phone. Still though, you should be fine.

Okay thanks guys ^-^ One it is!

Out of curiosity, what carrier?