One small point, your Vcc plane should be effectively grounded at RF (via the bypass capacitors).

As to your larger question - perhaps someone here will have some recent hands-on experience.  My guess is that you would want to keep your antenna away from everything else (including parallel surface ground planes).

The simplest way to make a 433MHz antenna on a PCB is to construct it as a track, clear of the ground.  It's length will be shortend by the velocity factor of the PCB dielectric, ie by 1/sqrt(Er).  Er will be from 2.5 - 4.5 on common PCB materials, so you need to find out what yours is.  Eg if Er = 3.5, then Vf = 0.534 and the length of your antenna element will be 53.4% of it's free space length which for a lamda/4 element @ 433MHz = 93mm.

You can further shorten the antenna by capacitively loading the far end to ground but this will need some more serious maths or modelling to get right.

Thanks guys, very useful. Appreciated.