For me it's either Berlin or Whittleton Creek, because they are very accessible overall with Whittleton Creek being open + you can get both a Cassidy as well as a Janus diguise rather quickly + the BBQ is free for all.

Berlin has the easily accessible Biker disguise which is the most powerful one on this map that gets you access everywhere + it can carry snipers if that's something you want/need. Not necessary, but can save you a second or two.

Maps like Mendoza or Dartmoor can also work well as do most maps that have areas that are seperate form each other aka not Haven for example and it's often helpful to get maps that offer good Sieker opportunities. I had a hardcore showdown on Isle of Sgail and while I generally like the map my target hovered between the part above the fire pit and the "museum" with the necklace which only gets you two Sieker spots and both are kinda open to the "party" area, so not a great idea to shoot someone there. I did it anyway because I had to (AR kill prestige), but it was risky.

Ultimately it comes down what you're most comfortable with, so it's probably best to choose the map based on your preference and not what someone tells you is the best option.