All formulas are either flat/matte or eggshell. Keep in mind that a specific shade will look entirely different from one house to the next. Lighting completely changes colors and paint swatches are deceiving. Because of their small size, it's tough to pick up on the nuances of a color judging from a swatch.
Therefore, my best advice is to test your favorite swatches using a paint sample. You can either paint directly on your walls (hit multiple places in the room so you can get a full perspective of how light affects the color...morning, noon, and night) or you can paint a piece of MDF or foam core board and move that around the room. Even though it looks horrible during the decision making process, I'm a fan of the paint-directly-on-the-walls approach. Home Depot's $4 mini sample jars are perfect for this activity.
Trust me...don't be lazy or cheap here. Get a few samples, especially if you are going for the perfect neutral. Grays, taupes, and whites are super tricky and usually have multiple personalities. It's hard to believe that the paint swatch I ended up using in the den was actually the color on the walls. The color that I initially thought was "the one" ended up looking lavender due to our overhead lighting. It was called Alpaca by Sherwin-Williams, shown first below. The second is the color I ended up using. The latter looks very beige-ish here, but on the walls it gives off a blue-ish gray effect. Very bizarre.
So, I ended up hauling the enormous 5 gallon tub back to the store to be retinted twice. It would've been much easier to have gone the sample route. Luckily, the den/kitchen was one of the first areas we painted in the house so I learned my lesson sooner rather than later!
My final tip is to use good paint. It will save you time and probably ends up costing the same as the cheap stuff because you have to use so much less of it. The Behr Premium Plus Ultra shown in the sample pic above is AMAZING. It's paint and primer in one. Just one coat covered the deep red paint that was in our dining room when we moved in. I painted the dining room and a bathroom with one gallon. The other added bonus with this paint is that the color swatch cards are large which is helpful :)
Enough with the painting pearls of wisdom...onto the tour!
Entry: Shaker Gray 1594 - Benjamin Moore
Front Guest Bedroom: Mindful Gray 7016 - Sherwin-Williams
Master Bedroom and Back Guest Bedroom: Slate - Restoration Hardware
Den and Kitchen: Senora Gray 1530 - Benjamin Moore
Living Room: Wheat Bread 720C-3 - Behr
Dining Room and Guest Bathroom: Fashion Gray UL260-6 - Behr Premium Plus Ultra
Study: Deep Silver 2124-30 - Benjamin Moore
Master Bathroom: Lighthouse Landing 1044 - Benjamin Moore