In short, a good d-pad is of utmost priority.

For as long as I've had a PS3 I have used my PS3 controller as my all-needs PC gamepad. Before I had a PS3 I just used a PS1/2 controller through a USB adapter I had. After playing the original Ninja Gaiden for a bit, I have concluded that the d-pad simply doesn't cut it. I like the DualShock 3 well enough, but the d-pad is really prone to sending diagonal inputs when you only want one of U/D/L/R, especially after having been worn out a bit from constant use. As anyone who has ever played Ninja Gaiden would know, diagonals often equals a horrible death (you can't jump off a wall if you're hitting a diagonal—yeah this is mostly just shitty design, but the controller doesn't help).

So I'm thinking it's time to get a controller better-suited for my classic game needs. The cheaper the better, but I'm willing to put some money into it if need be. I know that PS4 and WiiU Pro controllers work on PC/Mac, but I'd only consider those if the d-pads really are that much better, and I'm a bit skeptical, esp. for the cost (though I'll likely get a PS4 at some point in the future).

I was thinking something like this, though the build quality of these things are always super questionable. That particular one seems to get pretty high ratings though, unlike most of the others. Of course there are the USB adapters for actual SNES (or whatever) controllers, but most of those are so used by now that they aren't very responsive.

Any feedback/ideas?

That Buffalo controller looks like it might be perfect for your needs and it's hard to beat that price. I haven't used it though, so I can't specifically vouch for it.

As far as modern controllers go, I think the Dual Shock 4 is the best all-around as well as has the best D-pad. That said, the DS4's D-pad is probably not as good as what you'd have on that Buffalo controller or an actual SNES controller, so I'd recommend those first for classic gaming. You also don't need the analog sticks, triggers, rumble, etc. of modern controllers like the DS4. On price, modern controllers, especially new ones like the DS4, lose out again. Ergonomics is the main potential advantage of a modern controller, but that's a subjective consideration.

If you can find a real one, Sega made a USB plug and play version of the Saturn model 2 controller that works with PC and Ps3. Its the best d-pad ever made and its got 6 face buttons and 2 shoulder. Perfect for just about any retro game. They are not super easy to find but its possible if you want it bad enough. Just be careful of the KO's. Some of them are semi-decent but most are junk.

The madcats fightpad is inexpensive and works on PC like wired 360 controller. It has the layout of a genisis controller plus shoulder buttons.

The USB Saturn controller is alluring, though I don't know enough about them to know which are fakes. Just 'cause it says "official" on eBay doesn't mean a whole lot.

How are those gamepads MadCatz make for fighting games? I'd imagine the d-pads would have to be pretty decent since that's their entire raison d'être, but good god are they ugly.

@yummytreesap: its great, can't get much better. Price is also good.

I use mine for genisis and SNES stuff all the time. The turbo setting is good too for some of the button mashing those old games seem to think would be fun. The price can be pretty cheap so kind as you don't care about the paint job. They are almost always on sale on amazon.

I use a keyboard because I can switch directions more quickly with three fingers on WASD than with the less dexterous thumb on a D pad or an analog stick. Typical controller face buttons aren't ideal for a lot of classic games, since some controllers had rows of buttons instead of a diamond of four. Playing games that use all of those buttons can be confusing and complicated with a controller. For that reason I have them assigned to the two/three keys to the right of M and use the keys above them for controllers that had a second row. I don't use the same row as my directional "buttons" so that my keys don't lock up when I hold them.

@yummytreesap: You can tell by the price mostly. A real Sega made one wont be on ebay for 15 bucks. The MadCatz fightpad is supposed to be decent but I haven't used one so I cant compare. Heres a thread on Shoryuken comparing the 2.