My first Mac (a first-gen G4 Mini) was bought in a computer shop in a mall because they had a deal going on that included iLife and a Lexmark printer free. Apple did not have such deals then.
My next Mac, the first-gen White MacBook, was bought online because I had a Corporate Discount with Apple; and since then any new Apple product I bought has been online because of this discount. But I do go into the store to look, play (and lick too EhMax ) before I place the order online.
My latest Mac, a 17" souped up maxed out MacBook Pro was bought used around three months ago from an EhMacer who has since been lying low.
I voted for online, only because our online purchases have somewhat outnumbered our in-store purchases. You need to add a "both" option!
Our last two Macs have been from the refurb store - iMac for younger son, MacBook for older one. Prior to that was my G5, which I bought at the Apple store in Salem, NH when we still lived in MA. Good thing too, because it was one of the early models with thermal overruns and it produced them within 24 hours of taking it home. So, back it went to be exchanged for another - something you can't do online! I probably would have been stuck taking it in for repair instead - which wasn't always fixing the problem if I recall.
The G5 of course, eventually died (4 years after purchase) with the leaky cooling system problem and Apple replaced it with my current Mac Pro - an exchange that was handled entirely online and over the phone. I've had very good luck with the online refurb store, so could very well buy from there next time we need a new Mac. Hubby is next in line - his Powerbook G4 (last of the line) is getting very long in the tooth, and he may have to give in and get Framemaker for PC and run it under VMWare Fusion instead of struggling along on 10.3.9. Given that we do RAM upgrades and HD upgrades ourselves, buying from the refurb store often works out very well.
2.8GHz MacPro, 2.7GHz i7 Retina MBP and a bunch of other Macs and i-things