So many brands, so little money ... Aardvark, Digidesign, Cakewalk, Echo, Lynx, M Audio, MOTU, Steinberg (Cubase), Logic, RME, ST Audio ...
That's a jumble of hardware AND software you could consider, and I know there's more. It's so much more complicated than just "why not Aardvark or MOTU?" As had already been mentioned, you can get good quality from any of these.
It really depends on what your priorities are and what deals are available at the time. I went with a DIgi 001 b/c I knew one of my projects was going to be partly tracked in a professional PT studio and I wanted SESSION compatability, NOT just a bunch WAV files I'd have to import into some other software once I got home. And then I'd have to import all those WAVs plus what I'd recorded into that guy's studio, and frankly, I don't want to pay his hourly rate for that. That alone pays for the Digi in my case.
Look into the maximum number of simultaneous inputs you'll need. If it's just two, you have a lot of cheap options. Some cards let you run 2 audio + 2 SPDIF, which means with an external AD converter your 2-input card becomes 4, but some do not (Echo's Gina does, Digi's MBox does not). And what about card/software compatibilities?
Cost-wise, here's what I found for what I needed:
* I could spend about $450 for a Delta 1010 and, what is it now, like $400 for Sonar XL. That comes with decent plugins, but I'd want to buy another pack of plugins, $300. I could get away with the number of inputs on a Delta 66 card, but I've heard there are problems using more than 2 simultaneous inputs with some software I was considering, and I believe it was Sonar. Cubase was a possibility but then I heard from several sources that it has some serious summing issues which were to be rectified in the Cubase-with-Nuendo-engine release, but crikey, have you seen the price for that?!?
* I could spend $800 on a Digi, but then I'd STILL have to buy more plugins. OR, I could buy a Digi Factory for $1200 and get all the plugs I could need (yikes).
I thought of MOTU but the most attractive thing about them is Digital Performer, which, when I was researching, seemed to only be for Mac, and I'm on PC. I could be wrong on this platform support. DP would be the only serious software contender that could make me entertain importing and exporting individual sound files to that PT studio, because it's got nice features and MOTU users I know are quite happy and have produced some nice-sounding stuff without having to be rocket scientists. I have no experience with Logic but I've heard universally that it's hard to learn, so I shyed away from that from the outset.
I lucked out cuz someone local was selling a Digi 001 Factory, with receipt showing still under warranty and the thing was never even registered, for $750. Uh, I pounced on it. I'm wary of buying complicated (and expensive) stuff like this on eBay, so the local used market has to work for me.
Anyway, just some thoughts. hard to give you a definitive answer because everyone's needs are different. There are so many options it's mind-boggling, but your challenge is to find the best match of capability and quality to your needs and budget.
If you have specific questions about specific products, folks here are very helpful. happy researching.