Acrylic paint is a good type of paint for journals because it is so versatile. It is the paint I use most often. Generally it is opaque so that means when you add layers it blocks out the color underneath, unless you paint it on thinly so it can be transparent. The look you get is decided by how you apply it. It doesn't take too long to dry but stays wet just long enough to be wiped away or distressed if you gesso first. You can draw on top of acrylics with pencils and markers.
These are some of my favorite brands. I really like the Folk Art brand in journals because it dries completely matte. That means I can use colored pencils to draw on top of the acrylic painting like I did on this journal page to add fine details (click on the photo to see it larger).
The other paints in the photo above are the same as the folk art paint. They are all considered craft paint and are not as color fast as artist acrylics would be but I don't worry about that in my journals. I also like craft paints because most of them are non-toxic. A lot of artist paint is toxic and the toxins can be absorbed by the skin. I think it is something to consider if you like to paint a lot.
I don't buy the dabbers anymore because the foam pad always becomes stiff and unusable after a bit of use even though I cap it straight away. You also get far less paint in those little bottles than the other brands. If you do not intend drawing on top of your paint then other brands will be okay.
When I first started painting I was using these Jo Sonja's paints so I have a lot of them. They are an acrylic gouache so that means they have some chalk added to the paint. They dry super smooth but are a little more glossy than the Folk Art paint so I use them on pages where I don't want to draw.
A lot of journalers recommend Golden fluid acrylics. They are not a favorite of mine but I do use them sometimes. They dry glossy so it is not possible to draw on them. Even some pens won't work on them. I do use them on pages where I am not drawing because they have wonderful color. Most of them are transparent. You can see how transparent they are by that strip of paint they apply to the label over the 3 stripes. In this photo the Alizarin is less see through than the other paints. Note- some of the Golden paints carry a toxin warning so read the labels carefully.
These are the artist acrylics I use. They are very similar and I most often use them for canvas paintings. I consider them a bit pricey to use in my journals. The interactive paints don't completely dry for a couple of days so you can spray them with water and they will reactivate. It is great for removing color like I did in this large painting (where the light areas are on the rock).
When I want to add shiny paint these are my preferences. I like the Lumiere paints a lot because a little goes a long way. They are slightly transparent and glossy. If you do two coats they become opaque. The Stewart Gill paint is very similar but is a bit more runny. The Pearlescent liquid acrylic is usually thought of as an ink but it is a very fluid acrylic. It is fun to use for drips on a page. I consider metallic paints a finishing touch because it is too hard to work on top of them.
These distress paints are the only ones I won't recommend. They have a very bad chemical smell to them so I don't like using them. They are a bit glossy too so that means I can't draw on them later.
Watercolor paint is also a good choice for journals. If you want to use them in a traditional way with blending and shading then they need to go onto watercolor paper. They are not meant to work on gesso but in a journal it is a fun technique. They won't blend on gesso like they do on paper but are great for coloring in. I have used watercolor on top of acrylics too. They don't soak in like on paper so they are a bit harder to work with this way and very unpredictable but that can be fun too.
Quality matters with watercolors. The student grade paints don't have very much pigment in them so your work is a lot paler.
I got the Peerless paint after doing Jane Davenport's classes. You get a booklet with pages of each color. To use them you just pick up the color off the card with a wet brush. I cut a strip off each card and glued it to a piece of paper to fit into the back of my journal. It is handy for travel but as the colors are limited and you don't actually get much paint I wouldn't recommend these paints for journalers. They are magnificent for adding colour to black and white photos which was there intended purpose.
Brushes are an important part of painting. For journaling I like to use synthetic brushes because they are a bit tougher than real hair brushes and a lot cheaper. I use both white and orange synthetic brushes. I have never found any difference between them. In this photo I have a selection of synthetics on the right. I mostly use the flat brushes for covering big areas fast and the round brushes for doing details like faces etc. Get a few big ones and a few small brushes. The two brushes on the left are hogs hair brushes (super cheap) that I use when I want to make brush marks. The synthetic brushes make a smooth line compared to the rough line left by a hogs hair brush.
It is important not to leave your brushes in water overnight. The wooden handle will get ruined and the brush will come apart. At the end of every painting day take the time to wash your brushes out thoroughly with soap (I use dish soap) and let them dry flat overnight. Pay particular attention to where the hair of the brush meets the metal. This is where paint collects. If you leave it there it will make your brush hair splay out and become too hard to paint with. Your brushes should last for years if you take the time to care for them.
If you are not sure what paints you want to get I would suggest buying one color in each brand. You can compare them yourself and find the ones that you like to use. Pick a few colors that are favorites so if you don't get any more of that brand you will only have one tube to use up but it will be a color you really like.