One thing to be aware of is with bullpup rifles is that the gearbox and motor are right next to your head so it might seem "louder" because of the closer proximity to your ear than a regular rifle such as an M16, AK, or G36.
IMO stock accuracy means shit (although there are probably a lot of other people who think otherwise). Play with your gun first before you think of upgrading (even if it's a crappy Aftermath, although I'm not saying you should say screw it to preventative maintenance) but there are always things you can do to "upgrade" your accuracy. Using .25 or .28 gram BB's outdoors for starters, this will give you enough of an accuracy "upgrade".
After that it really depends on the quality of the hop up unit and rubber. Make sure you don't get any oil or lubricant on your hop up rubber and you'll be good (oil prevents the rubber from doing it's magic and applying friction to the BB so that it spins).
Another thing that you could do (but isn't recommended unless you're using a sniper rifle) is "washing" your BB's. This isn't recommended for most people though since there is a very high chance that you will tear your hop up rubber and have to replace it especially with people who are trigger happy.
Read the FAQ section on which gun you should purchase first. Remember the game is like 50% a fashion show so go with whatever you think looks more badass. That being said don't purchase crappy stuff that looks badass, think about enjoyment/comfort too. Are you comfortable reloading a bullpup? It might get some taking used to (I personally don't really like reloading bullpups but I probably could do it fluidly if I practised enough on one).
I would go with the SRC out of the 3 guns you listed there but if you get AV'ed I would go with a nice TM or CA ("proline").
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE