I just saw this list of questions at zzounds. It lists 9 questions, the first 8 of which I have actually considered in purchase decisions over my last 3 interface purchases over the past 12 years. The 9th one I've never worried about.

It is a great list of questions, in my opinion. Each of the questions should have some sub questions. For example, because I don't use a mixer and rely on the pre-amps built into the interface, I spend more time researching the available gain in the pre-amps, and signal to noise ratio for the preamps, and I do pay attention to user reviews of the preamps as well.

Question 4 probably should read - do I need digital AUDIO I/O?

Another question that I asked my last time around (just a few months back): Can the interface behave standalone; that is, does it need the computer to function or can I use it without? This is important to me because I use my audio interface as a crude mixer for rehearsing - I plug in my iPhone or .mp3 player which has the songs I rehearse with, and then my guitar or bass amp simulation, and use the headphone outs as a rehearsal tool. I do this less, as our band leader often simply e-mails us links to YouTube videos to practice along with, instead of my purchase of the songs, so I'm often connected to the PC anyways.

So, next time you see someone asking "What should I buy for an interface?", point them to these questions as starters. Zzounds Interface buying guide

Sweetwater Audio Interface Buying Guide also available, but I think this one at Zzounds does a better job listing out the questions.



===============================
Our Gear Picks + 9 Questions to Ask Before You Buy
In the home studio, your audio interface is the heart of your recording setup. Audio interfaces capture sound sources (like microphones and guitars), convert them into digital data, and send them to your computer's DAW software for recording.

Because your interface's microphone preamps and analog-to-digital converters can have a huge impact on the sound quality of your recordings, it's smart to invest in the best interface you can afford.

1. How will the interface connect to my computer? »
2. How many mic preamps/analog inputs do I need? »
3. How many analog outputs do I need? »
4. Do I need digital I/O? »
5. What about MIDI I/O? »
6. Does the interface have on-board DSP? »
7. What software is included with the interface? »
8. What's the interface's maximum sample rate and bit depth? »
9. What is jitter? Do I need an external clock? »
================================

My Songs, photos, writing,etc.
My Sound Cloud