First of all - try to be unique at all times.
The gameplay should be dynamic. Weapons scattered all over the map is good, because picking them up is instant. Keeps the game flowing. Also makes the players explore the map. Shopping weapons slows the whole game down.
Players shouldn't be allowed to spread out too much, they should be kept tight by limiting the area they can play on. A single limited map will get boring eventually so you'll need to change maps once in a while - do this with map rotation, maybe a voting system after a given time could be activated to select the next map.
There should be some kind of motivation for the players - a score they get at the end of the round based on their kill/death ratio or whatever. They could get some bonuses for the next round if they reach a certain score, like a medpack they can use mid-game or an extra weapon they get at spawn. This should keep one playing for a while, and it doesn't even require registration. Make up more of these and you'll be good.
As for the questions:
Which city you like and which one you don't like (why?)
Basically I like every part of the SA map, with the single exception of Los Santos. It's just messy, and I don't really like that whole gang setting. But that's just my own preference, if you want to make most players happy than you'd better add a map rotation.
Do you like fast car tuning (for example by typing /tune)
I don't.
Do you like fast weapon buying (for example by typing /deagle)
No. You'd better make a location-based shop - like a checkpoint, or better yet, lay random weapons across the map - it's a deathmatch server after all, isn't it? No time for shopping. 
Do you like when you spawning full of weapons and/or armour or you like to be clean?
Neither. Don't go extreme. Give some basic weapons to the player at start - one of all type for example - and let them collect the more advanced ones themselves. And armour, I like it when you get it at spawn.
Do you like stunting zones?
I find most stunts boring, because they're all the same - high ramp, infinite loop or crazy sky-road, which you'll eventually end up colliding with while flying your pretty Beagle - aww, poor plane. 
Which your favorite weapons?
I prefer katana for close combat and the combat shotgun, the mp5 and the silenced pistol for ranged. I don't like dual weapons for some reason in SA. They just don't feel right.
Do you agree RPG/Minigun weapons on a server?
RPG only if it's rare and comes with a few rockets only. Minigun - absolutely not.
Do you agree Rhino/Hydra/Hunter/Sea Sparrow vehicles on a server?
Hydra and the Seasparow are okay.
Do you agree Teleports on a server (for example /ls /sf /groove /stunt)
During deathmatch, so players can escape? No, I don't.
