What principles are used to pick the 1v1 ladder pool? Without a clear idea of fundamental principles, the ladder pool will be a mess like the current one. Well, the topic does invite us to "let loose".
The ladder pool is poor because there are too many maps, too many bad maps and too many large maps. Each of these points is just an opinion without backup reasons of course. The reasons come out in an analysis of basic principles. Let us start from scratch.
First, FAF is a really difficult game. Players rated over 2,000 might not think so but the rest of us do. I would equate playing FAF to playing chess on a 100 x 100 board with about 1,000 different pieces. That's the difficulty level. If the map pool is too large it's hard to get competency in enough maps. Map rotation is the way to get map variety over time.
But back to basic principles. Some of these are obvious I know. All maps should make the grade on all these criteria before being selected.
(1) No bugs, no glitches, no serious pathing problems and no balance problems. (One of the obvious ones).
(2) Visual clarity. Maps must present visual clarity so that players can see and assess terrain.
(Ground that is too dark or water that is not clearly water are two obvious and common problems. Terrain and water should be visually clear.)
(3) High level of art design. Some maps just look too amateurish and often these are the ones that suffer from problem 2 above.
(4) Complicated in and outs of terrain should not be too extreme. For example, maps full of narrow and blind canyons are a pain in the ass.
(If there is to be one of these in the pool, make it just ONE.)
(5) Single mexes scattered everywhere is usually a bad map design as well.
(6) Excessive reclaim really distorts game play. Keep these maps in pool to a minimum.
(7) Keep the overall pool manageable at all times. I would suggest no more than 8 to 16 maps (something in that range).
(8) Good mix of small (5x5), medium (10x10) and large maps (20x20).
(4 small, 8 medium and 4 large would be good.)
(9) Good mix of maps for each faction.
(10) Good mix of maps that favor land, sea and air respectively, plus ones that allow balancing of these forces.
(11) Avoid maps where luck (or skill) of an early snipe (e.g. of an air transport with 6 or 8 engies) sort of determines the whole game after that.
(12) Avoid too many large maps where the mex groups are so common they are clearly really 4 player or more player maps.
Actually, any map not made by the original makers which is used should still be up to the original design standard or close to it. Tag Craftious Maximus and Loki are examples of good user-made maps. They look good and lead to interesting and fair play. I could name some really bad maps but I don't want to offend anyone. There are originals that people hate like Vargas Pass (IIRC). The really dark terrain one. It is actually interesting to play. Just hard to see terrain. Maybe one dark one (black or very dark red terrain) in the pool at any one time is enough.