The deagle is preferred because everyone see's it as 1337 pro weapon. However most people can't use it like that, only very few can nail one deags constantly to be confident with it. I'm currently training with my deag so I'll put deagle.
Deagle
Nuff said
My first vote went out to Glock, but I'mma go into more detail now.
1) Glock: High rate of fire on semi-auto...not very expensive (for scrims) and the default T pistol. If you can aim for the head, you can use this gun. Burst fire isn't so great to me, but it also has it.
2) Dualies: Again, high ROF. They are powerful and get good headshot kills. These also have a fairly good range, even when not crouched. Not much kickback, either.
3) Desert Eagle: By far the favorite pistol in CS:S. If you are good, you can get a one shot one kill with this, and it does good damage. Lower ROF than Dual Elites or Glock.
4) Sig P228: Awesome gun! It is capable of a one shot one kill (on a person with 100 hp) but this is VERY VERY VERY rare. This has one on the highest ROF's, and is quite powerful. <3
5) Five - Seven: I love this gun, but it can't beat the ones about it! Yet again, if you can aim for the head, this gun is a breeze. I personally HATE the default skin for it, but that is easily resolved. VERY high ROF.
6) USP: This gun is the standard CT pistol. A big point is that it has a silencer, so it is good for us ninjas out there. It has a fairly high rate of fire, and does about the same damage as a Glock.