Talking about the portable itself, analog and button placement.  The ergonomics of the system and how easy it is to do what you want playing different types of games. 

If you have a PSP and Vita, get them both and it'll be easily noticeable.  The buttons are larger and the button placement is further apart.  Both systems have the same space to place buttons, but everything is just so close together on the Vita.  The analog sticks on the Vita are way too close to the control pad and buttons.  If any of you play Wipeout 2048, I'm sure you've probably did a u-turn when you didn't want to because you ever so slightly touched the right Vita analog stick.

This has been one of the things I haven't liked about the system day one, but it's not been much of an issue because it didn't interfere much with the types of the games I've been playing.  Today I just downloaded the PSP version of Tekken 6 and trying to play that game on the Vita makes it all the more apparent about how much the proximity of the buttons to one another just really sucks ass. 

I know it was an issue to some, but I feel like promiximity of the buttons are far more detterent than the analog nub closer to the edge of the system.  I quickly got used to using the analog nub where it was located and I'm sure I would do the same for the analog sticks.  The PS button and start, select could have been moved to the bottom where the PSP had its buttons, surrounding the label PSVita.  Would have been an all around better design in my opinion. 

*edit*  Adding picture to show comparison of the buttons/control pad.

While playing Tekken 6, doing directional attacks were fine, but doing quarter circle attacks with the small buttons on the Vita were almost impossible doing so towards the left.  I have no problem doing it on the PSP or the PS3 controller, but on the Vita, the left analog stick gets in the way.

The spacing on the buttons and the size of the buttons make hitting buttons like triangle and x at the same time impossible without using two fingers, index and middle finger for example, while on the PSP or PS3 controller, you can hit triangle and x together with just your thumb.  It's also easier to hit any of the other two buttons together because the buttons themselves react better.  More than a few times I attempted a grab, both kicks or both punches, and failed on the Vita. 

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People can say what they want, defend the Vita, but it doesn't change the fact that the buttons and analog sticks are way too close.  This isn't some Vita vs 3DS dick measuring contest, it's that the Vita is far worse of a controller than the PSP ever was.

Go play a fighting game on the Vita and you'll notice how much of an issue it is.  Or if you have yet to play it, play Wipeout 2048 and play eliminator mode.  I guarantee most of you in five plays of eliminator or less, you'll accidentally do a u turn because the analog sticks are too close to the buttons as well.  Playing normally, not sucking at it just for the sake of not accidentally doing a u turn.

It did start to feel a little uncomfortable after an hour or two of playing. The overall design though is nice and sleek.

I thought it was the same thing

Start and select are horrid. I use the PS button instead to pause a game. Otherwise I got no beef with it.

Well, it's all personal taste at the end of the day, I've never played with a PSP but I don't find Vita's button placement too difficult to manage, plus it has its advantages especially when you need to press 2 face buttons at the same time, for example when using Hyper Combos in UMvC3.

Stick placement I'll agree isn't perfect but it only really bugs me when I want to use the back touch and even then it isn't a dealbreaker, so I guess it's one of those things, you can never design a console or controller which perfectly suits everyone

My biggest problem is the back touchscreen, if you're playing a game that requires you to use R2 and L2 buttons a lot like MGS1, it makes holding the Vita really uncomfortable and bringing up the weapon and item menus kind of a pain.

The buttons are a bit too close together/small but overall the system feels extremely comfortable in my hands, much more than any previous handheld IMO.

So it's more of a maneuverability than exterior design.. It is true that buttons are smaller and closer than PSP's. but it's that 5 inch screen's fault..

I thought PSVita was pretty good when it came out to be honest. Little better than PSP and much better than any Nintendo DS to date.

However once you have Nvidia Shield in your hands nothing else compares in terms of comfort.

This might seem the logical explanation, but that's not the reason, the Vita itself is also wider.

If you take the PSP and Vita and place them together where the screen matches each other, where the buttons are on the right and left side have the exact same area space.  The reason why the buttons are so small on the Vita is because they put the PS button, start and select, and the additional analog stick within that same space. 

I added a picture to the topic post.