Not all wood is the same, so you might want to research and decide on this or that type. My personal preference is the dark heavy wood, it sometimes goes under the name of ironwood, or mangrove root, or jeti wood. But it is very dark-brown almost (if not actually) black [you can see it in my tank photos], and being heavy it always sinks. It releases tannins like all wood, but minimal compared to some. It does not quickly rot, and plants grow on it easily (Java Moss, Java Fern, Anubias). It looks very authentic underwater.
The lighter wood, mopani wood, is bad for tannins, will float until it is thoroughly waterlogged or somehow held down, and often has bacteria that initially can cause problems.
Another thought to bear in mind is that wood of the same type in a tank looks more natural. It takes a bit more effort to get a mix of woods to look natural.