The PS Vita is about as strong if not stronger than a PS2. It also has two analogue sticks, unlike the PSP. While it may have a smaller screen than what you get on a console with a tv, it shouldn't be that noticeable since you're holding the handheld closer to your face.
Also in terms of games in the HD collection, Peace Walker was a portable game in the first place, so it is intended to be played on a handheld anyways. MGS 3 was also ported to the 3DS and got good reviews. The only game that wasn't intended for a handheld was MGS2, but still it should be a lot better on the vita than it would be on a regular psp. Finally the Vita lets you play the original MGS if you buy the psn version.
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