dittoLet me preface this by saying that I have been a real Honda guy in the past. I worked for an Acura dealer for years and have owned various Acuras and Hondas. I bought my 6 because it was more engaging to drive than the Honda Accord , plus it came with a manual tranny and V6 (Honda did not do that until last year). I am familiar with and have driven all three of the cars you are interested in. I'll go down your list:
1) Probably advantage Honda, but my '03 6s w/ 49k miles has been a good car
2) How often are you carrying adults? 6 and Accord, nearly a tie - the 3 is smaller, but ok for 2
3) All three are very good overall
4) Advantage Honda (it's not huge, but especially on interior materials, fit and finish)
5) All three are equal here
6) Wind noise is pretty equal, Honda has an advantage in road noise isolation
What you need to be asking yourself is "do I need a midsize, or compact car?" You are comparing two brands that have similar flavors, but the Mazdas definitely have a clear advantage in the fun to drive factor. So, are you looking for a more engaging driving experience? If so, then either Mazda will fit the bill - the 3 offering the highest advantage solely because it is smaller, more nimble and has the same 4 cylinder moving less mass than a 6. The Honda is a nice car, but the Mazdas are, too. Plus you get a 3/50 limited bumper to bumper warranty and a better deal ($$$) on the Mazda, so there is a value advantage as well.
Good luck on your decision!
just would add that traction control is a big bonus for safety - i think this is standard on the 6 and not avail on the accord i4. also, brakes on the 6 are better. plus if you get the hatch version of the 6, you get sedan styling with a huge extra dose of functionality. I drove the accord (been a big honda-fan for quite some time) and felt that the 6 was just more fun to drive without sacrificing much in terms of reliablity. the deals available on the 6 right now are pretty outstanding, so the value proposition benefits the 6 as long as it's characteristics are in line with what you're after.