which head

i just got a manfrotto 390rc2 with my manfrotto o55xprob, should i get the Manfrotto 488RC2 ball head instead, is a ball head better then a 3 way head???

Yes - ball heads usually better than 3-way heads...

For most applications, a good ball head will allow you greater control than a three way head.

However, the very best ball heads incorporate Arca Swiss Compatible quick release systems. IMO, these are the best, although the most expensive, way to support a camera.

Another way to go is to use the 488 ball head and add a RRS or Kirk Arca Compatible quick release to the 488. Using an Arca Compatible QR, you can mount your camera with an L-plate.

I am a great fan of the L-plate system such as produced by Really Right Stuff.

http://reallyrightstuf​f.com/QR/05.html

just not sure if i should take back the cheaper head and get a ball head or not, or is the head i got good enough

You will probably find that the 488RC2 is a lot sturdier than the 390RC2. You may not notice the difference with lightweight camera/lens rigs and with shorter focal lengths. However, with longer focal lengths and heavier equipment you will easily notice the difference in rigidity.

In addition, a ball head is often a lot easier to use than a 3-way head for everyday still photography.

If you have a lightweight movie camera or video camera, then keep the 3-way head for that - assuming it moves smoothly when you loosen the controls for panning.

I use the Manfrotto RC2 quick release system almost exclusively and have not had any problems that would make me spend a lot more money for the Arca-Swiss style QR system.

If you are going to use it to shoot "still" subjects like landscapes, portraits or macro, where precise framing is required then a good 3 way head such as geared one is the way to go.

The less expensive ball heads, anything less than an RSS etc. or similar will move it's position on final tightening, up or down (depending on the head), or the whole rig will droop slightly when you let go requiring reframing. I have neveer tried the 488 but I imagine it behaves like what I described. Anyonwe can chime in if I am wrong.

On the other hand, if you are tracking moving subjects, any ballhead is probably better than a 3 way head, imo.

I had a 3-way at first, really found it too slow to adjust. Go with the 488, its what most here have and its a great head!