Hi @Dreampainter,
A warm welcome to the Bunnings Workshop community, it is wonderful to have you with us.
The best tool for applying paint depends on the context it is being used in.
If it is a base coat of colour, I'd suggest using a small foam roller like this UNi-PRO 85mm Little Ripper Mini Foam Roller Cover And Frame. This will produce a nice, smooth coat that can be rolled on quickly and easily.
If you are looking to do slightly finer work, use a long-bristled brush such as this Monarch 38mm Walls Doors And Trims Synthetic Paint Brush. This will be handy for adding detail to the mural that doesn't follow directly along the ridge lines.
For very fine detail, you can use craft brushes like these Crafted Assorted Paint Brushes.
If you are concerned about brush marks or overlap lines, you can add a paint conditioner such as this Flood Acrylic Paint Conditioner to help smooth things out.
Let me know what you think, and if you have further questions, please don't hesitate to ask.
Jacob
