There are a few reasons the current S2 map doesn't work, in my opinion. One is because it's big and has limited hiding spots. More days often than not, you'll find the top hiding spots are places like that single big house in the little cul-de-sac, or the nightclub, or the parking garage, or one of the warehouses. That's pretty much it. They introduced Rockford v2 and it just didn't change a lot, just made things slightly prettier, and even that's debatable. It's good for mining, but not really too amazing.
Evilmelon would be a bit of an improvement because at least it has areas which are more appropriate for basing, and it's got a lot of potential for further greatness. The mining areas would be easily added in, it's easy to drive around - save the people randomly raising the bloody bridge every five minutes - and it's got a few good places to run a shop, too. Players who want to be mutants will also have a place they can actually work in, etc.
There are a couple downsides to this map, like a minor one being the acid in the sewer/train area - it's easy to exploit that area for an easy hiding spot, and some people will print there even when there's a rule in place against it.
A more prominent downside is that a couple of the buildings are very one-sided in their design in terms of raiding, I think one of the buildings has a basement area that you can go into and they can easily booby-trap the hell out of it and wait there with their best weapons and just wipe out raiders en masse. That might just be me being noobish, though.
Bloc42 had problems that just can't be overcome, now. That map was what set this server apart from the rest, in my opinion. I think that while it is possible to work on those problems, and potentially revive the map, it would require time and resources that just aren't worth getting rid of a perfectly good map for - plus, if you screw it up, you've got a whole server whining at you about it. Lol.
Bangclaw isn't widely used. I think of all the maps I played on? Bangclaw was one of my favourites. But I think in terms of sustainability - bangclaw is a decidedly small map in comparison to most. Bangclaw has fewer buildings than most, but it makes up for it in terms of being quite a "strategic" map. You need to think in order to actually base in it, and the massive sewer area is the biggest of any map I've seen used, so far. It's got limited usage - no English speaking DarkRP servers run this map, anymore. Which might pull in a bit of interest from new players, too. Plus, you know. It's a pretty customisable map, and there's a lot of room for craziness.
On the downside, basing can be tricky, and even basing "strategically" can be a challenge because a lot of the housing is quite small, and more often than not, you'll have people with the explosive weapons of varying types capable of easily busting into the bases, no matter how well-defended they may be.
Also, while there are a great load of hiding places in Bangclaw, it also makes for a lot of exploits, too.
Evocity would probably be my choice. This map is too big. Like, it has a lot of crazy stuff that makes basing an absolute craze-fest. But it's also a lot of fun. It also depends on what evo you use. I think using evo makes for fun basing, a more competitive and active environment, and again - it's not widely used. Again, no English speaking DarkRP servers use this. You've got a water area, a big police department, a nice office for the mayor next to the spawn and up a lift, a lot of buildings that can be used for basing and printing. This one also has a little cul-de-sac, if I remember correctly. There's just a lot to like about it.
The things that drag it down are the fact that it's too big, the fact it has a lot of crazy hiding spots that admins might not always be able to check for abuse, the fact that it's got a lot of exploit points, etc. I don't think it has an area for mutants, though I could be wrong.
These are just a few basic points on each of the maps people have mentioned. If the owners do notice this and decide to take it in a different direction, they could even consider making their own map, or hiring a new staff member to design a map for them or something.
And it's really just my opinion. Nothing more to it. Thanks for reading if you got to the end.