Yes, on all of those maps, both sides have good places for a base, they can easily move around the entirety of the map, and there isn't any crazy shit that favors one side or the other.
What makes a map unbalanced is
A: One side has a clear advantage i.e. very open flat spaces with little cover (favors humans) or very tight halls too much ground clutter, or large portions of the map are inaccessible to walking classes (favors aliens)
B: Base locations are restrictive for one race or another, or poor staring base area.
All of the maps i've mentioned have at least decent starting base areas, and if a knowledgeable builder works diligently a base can be quickly made and then improved to last the entire game and give your team a solid fallback to work from. They also can be moved about in by any player who isn't a total noob, and they don't have a ton of crazy shit that makes them hard to learn and understand, they're free of glitches and they don't favor one side over the other in terms of layout and movement.
Granted new players who try building, people who build 1.1 style bases, and gaps in skill tactics and teamwork will make maps seem skewed to one side. It's harder to build a good alien base on nano than it is on say... niveus or in the elevator room of karith but it can be done with some thought and planning.
For example: I'm going to pick apart the map 1984 since it's the most recent one i've played that has annoyed me
1984 is an alien-centric map because starting out dretches can very easily access the roof areas and move freely around the map without much worry of being shot at and, as humans have no way to track them it makes it very difficult to play actively, forcing a camp in one of several locations or what will most likely (if the aliens have any brains) be a huge feed, then at s2 humans get jetpack... which does almost nothing because a dragoon can easily pounce from building tops and take them down... there isn't really any alien class that will have difficulty moving about in the map other than tyrant, but all humans are essentially restricted to the ground if aliens do their job. The helmet helps prevent ambush but it's also a marginal benefit because there is only one path to the roofs and the aliens can easily restrict humans access to that path. The humans starting base is a POS and the starting base area is also very poor. There isn't really a GOOD place for a human base only decent ones.
Now lets look at a good map: UTCS since Asvarox is raggin on it
The starting areas for both teams are good places to build a base, secondary base locations are not very good for either side but i've seen some ok outposts or even a good move or two on this map, the center location is fairly open but for dragoons this isn't much of a problem, and if you adjust your tactics accordingly, try to attack in the halls and use surprise maras, basilisks and dretches don't have too hard a time, tyrants... eh, depends on the situation but I don't tend to use them much, humans will make good use of the rifle, las, and md, using the distance of the center and openness of the halls to their advantage. Both teams are on fairly equal ground and if the difference in skill is not too big, and if the proper strategy is used it can be a nice long match that is fun and fair.
If you look at it this way... if it takes a substantial gap in skill, teamwork, or tactics for one team to beat the other on any particular map, it's not balanced.
tl;dr: good maps have good places for bases and a mix of open, and tight terrain, or have a layout that is sort of "between" tight and open all over, they are for the most part accessible to both humans and aliens at s1 and neither race will have problems moving around them.
I was mistaken about it 1984 being in the rotation
i'd suggest adding UTCS into the rotation. As for balancing it on a wide range of maps, yes I agree but some maps are just... well kinda dumb... I don't wanna play rotcannon, crazysurf, lowrise, or any of those maps that have confusing teleportation systems and way too many tunnels on the official server unless a bunch of people vote for them.
Anyway that's just my opinion, I try to be as logical and explain as well as I can.
