Well first off your two choices are mighty fine. Can't go wrong with either of those choices. The MAK is a great choice also. I am partial to Memphis because I own one and IMHO it lives up to the "Grill" in pellet grill due to it's insulated design and high temp range.
The first suggestion I can make is that if you get a chance try and visit a dealer to check one out in person. And even better get a chance to cook on one.
You are going to get many different opinions on which grill is best and the final decision will be your's alone.
Consider how much pellets cost in your area. If your grill is a pellet hog then those costs should be considered. Hands down the Memphis has the lowest pellet consumption of any grill out there. I have personally had winter time overnight cooks that used less than 1lb an hour at 225F. Some grills cannot get under 1lb an hour at any temp anytime of the year. If you have access to an abundant amount of pellets for cheap than that will be less of an issue for you.
Also heavy gauge steel is great for durability but not so great for pellet consumption. There is a lot of heat loss trying to get all that steel warm and then when the cold wind travels across that metal the heat loss can be tremendous. So you might want to add the cost of a insulated cover for winter cooks when buying a non insulated grill.
Size can be important. Getting a grill that is too small to suit your needs might not be a good idea. There are times the larger capacity will come in handy. The MAK is really nice because of the large domed lid allowing more room for butts and whole birds. Higher capacity will save you money because you can get more food cooked using slightly more pellets.
The controller is important to keep consistent temps and create smoke. Both the Memphis and MAK have high tech controllers. The MAK surpasses in this category with the Pellet Boss.
And materials can be an issue. Powder coating will peel and bubble if over heated and will degrade over time. The Memphis is all stainless. I mean ALL stainless. I have no worries about rusting issues and mine when cleaned looks almost as good as the day it was delivered to my home.
So do your research and if you have more questions just ask and we will all be able to confuse you more on what to buy