When I fill a parametric brush circle it has white lines.

This I want it to not look pixelated too I am using the brush not the pencil.

This is not what you get with the brush, this is the display of the brush in the Toolbox or in the Brushes palette. The results of the brush stroke are smooth:

Looks like a different problem. From what I see:
- you made a closed loop with the brush
- then you used the Bucket-fill to fill the inside using the "Fill similar color" options

So this isn't a problem with the brush... this is a problem of the "Fill similar color" option not dealing with the anti-aliasing pixels (ie, the partially colored pixels at the edge of the initial stroke). The color selector and the fuzzy selector don't deal with them either. See the whole story here.

For what you want to do:

1) create the closed line on a transparent layer
2) make a fuzzy selection clicking inside the line
3) Select>Grow the selection by two pixels (so that the "ants" will be slightly inside your line).
4) Add a transparent layer below the one with the line
5) Bucket fill the selection (ie option: "Fill whole selection", not "Fill similar color"). This will make a color spot larger than the inside of your line, but your line will cover the 2-pixel "bleed".

Alternatively, everything on the same layer:
4) set the Bucket fill in "Behind" mode (using the selector at the top of the Tools options):
5) Bucket fill the selection, on the same layer as the line. The "behind" mode will make the painting happen as it it were on a layer behind the active layer.



Best keep everything in distinct layers, it makes later changes much easier. Save your image as XCF to keep the layers, use export (PNG) to show the world (merging the layers is automatic when you export).

Faster way of coloring the fuzzy select doesn't select all those whit lines and besides I want a really fast way of coloring without seeing those white lines.

Ofnuts, thank you so much for your clear extensive explanation to the problem. I learn so much from you and people as you teaching and solving problems in gimp.

Maybe I said that because I want to know how to color something without those annoying white lines.

Well, you have been told how to. A quicker technique is to make a selection to paint the inside first, then use the selection (Select>Border, or Edit>Stroke selection) to draw/paint the border. But that requires a bit of planning ahead.

Quick, clean, thoughtless, pick any two...