So firstly what kind of painting are you hoping to get into? Secondly, what surface? This can affect your choice of paint. Regular art on paper/board/metal/ or t-shirt/textiles, or automotive etc, etc. Also the style in which you like to paint may affect not only the brand, but the type of paint you choose. For example opaque, semi opaque, or transparent. It sounds to me like you are currently using opaque as that tends to give a flatter finish (and to me can also have a chalky appearance depending on the surface used). The advantage of opaques is that no matter how it is reduced, with enough layers it will completely cover any layer below, and will only ever reach the colour you see in the bottle, and once at that max saturation will not get any darker. Semi transparants take longer to build, so are easier to retain translucency, but again will reach a saturation and coverage point. Transparents have the most 'pop', and colours can be mixed on the surface (giving almost infinite colours and blends)- i.e spraying yellow over blue will become green, as the layers below will show through. It will not cover what is below, no matter how many layers are added, except that eventually the colour will continue to deepen until it reaches black.
I choose a mixture of paint types. An opaque black, white and red (as trans red looks pink until many layers are built, and sometimes I just want red) and trans primaries. With these five colours, and combination of opaque and trans I can mix everthing I need. However for laziness sake I also have a trans sepia - just because I like it, and use for underpainting also, and a trans fleshtone ( which despite the name is not going to give you a convincing skin colour, as skin is actually many different tones, but is a good base to start from), which I find useful for mixing earthy tones.
The brand you choose, and different categories of paint within that brand is down to personal choice, how you like to paint, what is most suitable/which you find you take to better, and what is easily available. To add to the popular choices listed above I will include Grex (also known as E'tac).
Some paints are suited to specific tasks eg. auto air - for automotive, createx - fabric. However createx illustration or E'tac efx are primarily used for fine art/photorealism. My particular favourite is another branch of createx, which is Wicked. I like to paint on many surfaces from fabric to auto, and anything in between, so I choose Wicked as it's an all rounder - not specialized for any particular surface, but can be used on almost anything. I believe E'tacs PS range is a similar equivalent.
You must also factor in use of additives to your brand choice. Some brands reduce with water, Createx has it's own reducer, which I thoroughly recommend as it has many other properties which aid airbrushing, such as faster drying times, harder cure, less surface tension to prevent reactions such as fish eye, flow enhancer as it emulsifies the paint, and also when reducer/paint ratios are finetuned negligible tip dry, very low chance of blackages, and used as a final spray an excellent cleaner. (If you go that route, I really recommend buying a larger bottle, you will use it, and it works out much cheaper). Also your choice of paint may want to take into account it's lighfast capabilities, some have excellent uv protection to protect work from fading.
Hope this helps you narrow down your options. It is worth contacting suppliers to ask for samples of paint - although you will have to buy any additives that are recommended, this may help you make a final decision.