Nades or better gun?

Whats more useful to get, lets say a famas and full nades or an m4 with less nades?

Depends on how good you are and your playstyle. If you know a lot of nade spots and are really good with them, nades. But if you have really good aim and don't know nades you should get a good gun probably.

use the boom to kill the idiots..

nades cuz u can smoke and throw moly,so u can easier enter the site,if u ct u can throw moly and stop the rush

I suggest you upgrade your current gun and use the extra money to spend it on nades. However you might have to get the nades to assist your teammates

If you get more grenades, you can retake, IE Ninja defuse, flash defuse, Molotov defuses, grenade defuses and so on, if you have a better gun and the enemy flashes you or doesn't peek at you, you're dead.

it depends entirely on the map, and on what position you're playing in, for example, if you're gonna hold B site (in mirage) then I suggest you choose the Famas and nades,
but if you're in a more vulnerable position such as on A Palace then I suggest you buy an m4 with a minimum utility such as a flashbang or smoke, as those 2 nades will be all you'll need to either smoke a molly or to provide sufficient help to your teammate.
(friendly reminder, never buy if you have less than 4.5k dollars on the Counterterrorist side)

Utility is super-important in this game, so I would say FAMAS + full utility. Try to take closer fights, at short/mid distance FAMAS is basically the same or almost as good as M4.
Of course, in solo-queue people are just running around like it's DM anyway so M4 + no util can still work if you can outaim lol

Depends on your skill with the gun. I would personally choose whatever gun I am confident with, even if that means not having money to buy more nades.