Which of these cars should I get as a first car?

Mazda6 2012
Toyota Corolla 2010
Honda Civic 2010
Toyota Camry 2010
Honda Accord 2012

Assuming the mileage isn't too high and the price is reasonable, I'd go with the Civic as my first choice and the Corolla as my second.

It would depend on which has the combination of best condition, best features, lowest mileage, and lowest price. Assuming they were equal (which is impossible), the Civic would be a good choice.

The Camry or the Accord. Both are very reliable, have plenty of room, get great mileage, and ride and drive comfortably.

They're all generally good vehicles.

But as they are used, any vehicle you are seriously considering buying should be first inspected by a dealer or other trusted shop of YOUR choosing before finalizing the deal. It will cost you a little bit extra but it's well worth it as it greatly reduces the chances of you being stuck with unanticipated repairs within the foreseeable future.

Get someone who has a clue about cars to go with you to LOOK at the cars and TEST DRIVE them. They are all used. They might ALL need a new engine or transmission and you are SOL if you buy any one of them.

Well you have two distinct body sizes there. Get the car that's right for 80% of the driving you do. If you don't need the extra cabin space, get the Corolla or Civic (or Mazda 3). They are all available as hatchbacks and can also carry a lot of stuff in the back if you need to - just fold down the back seats - but will be cheaper to run when you are just doing the 9to5 commute to work all by yourself. If you habitually carry two or more passengers, get one of the larger bodied cars. Be aware these have sedan or sedan-like bodies, and while you may still be able to put the seats down, you may not be able to carry as much bulky cargo because of their less boxy shape. Bigger cars are more expensive to run but are more comfortable for passengers, though the smaller hatches may carry a greater volume of stuff if you use the load area to the max. My preferences; 1. Mazda, =2. Honda/ Toyota. But take some test drives and get the one you like best. They're all good brands.

Drive them all to see which fits you best.

Buy the one that is in the best mechanical condition, with the lowest miles, that preferably has only had one owner who isn't a teenager and who has maintained it regularly and kept detailed records and receipts. If you don't know how to evaluate the mechanical condition of a vehicle, pay a shop to look at it for you. That's always money well spent if it prevents you from making a mistake.

They are all generally good cars. Civic & Corolla are smaller than the others and you did not include mazda 3 which I have.

When I was searching a few years ago, I wanted toyota, honda or mazda whichever I could find the best deal on.

It ended up being a Mazda 3 because I found a government auction on one an hour away.

Later, I was using a US News & world report and I found a lot of people who had corollas had complained about the acceleration. I never drove all 3 so I could not compare. But I know my Mazda has great pickup.

Also, generally, the smaller the car, the lower the price. So a mid size is going to cost more. I almost wish I would have found a mid size but I'm not trading cars over it. My 2012 will probably last me 8-12 more years if I live that long. Although who knows, as I get older I might get a wild hair and upgrade sooner. It's not like I can take it with me. My car only has 55k so Its hard to see it not lasting a very long time as I don't drive much.

Can't imagine upgrading for at least 3-4 more years. Even with a wild hair.

It's best to avoid car dealerships to save money. Take at least a 30 minute test drive over a variety of roads and if you still like it, have a mechanic look it over.

On the cars mentioned above, you can reasonably expect to save $1500-2500 by avoiding a car dealer.
(that's why I did not buy from one, and I was a low end car dealer for a dozen years, way back when)

(I no longer have access to dealer auctions and did not feel like hitting up old friends to get in, although I could have probably)

Id do all that before my comment but also consider which car gets stolen more. Insurance cost and don't forget to look up the cars vin #'s for vehicle's history!