Is the best weapon for a noob the jester something? or is the rifle u buy in the store better?
i have the rifle and i hate it. it can only kill weak snakle things, nothing else really.
the best gun to use depends on what you are willing to spend.
f.ex an big rifle (50+ dmg/sec ) isnt really good for snable killing. better for atrox. now, atrox hit harder. so, then you need better armor and fap. which is big bux, and decay.
Use the trade terminal to buy a Sollomate Opalo. It’s roughly the same gun as a jester but will operate at a higher effeciency. Yes, it’s small gun which you can only really use to hunt small animals… You can get a bigger gun but you’ll use it quite poorly and it’ll cost you much more ped per hour of gameplay… That choice is up to you. 
The key here is to start small and grow your skills such that you can effeciently use bigger weapons.
..
ive got a L/Murdand Groover got it free and im on lvl 19 with it now
Depends entirely on your skill level 
I wouldnt buy anything to expensive when you are starting out until you have the skills to use it’s full potential, otherwise you will just be wasting your money. A good starting gun is a jester/outbacko/opalo, then when you have reached a high enough skill level you can upgrade to something a little better. You will have to start with some of the smaller mobs at first with guns like those, but eventually with skill and better weapons you will be able to take on the big guys : )