Trimboards on the outside of a house always seem to need repainting before anything else. Or they rot. I used PVC trimboards on my house to avoid these problems. Azek trim is solid PVC. It can't rot and is manufactured white, so painting is unnecessary. Azek is very expensive, but you'll save on future maintenance.
Azek has several trim products. I used the Azek Traditional Trimboard with a smooth finish; 1" thickness. 6 inch width was used for fascias and at the eaves. 4 inch width around windows and doors. We also used the pre-formed Azek cornerboards. They're very easy to install and the corner seam will never open. I chose the 6" corner size. Azek trimboards come in long 18' lengths and the cornerboards come in 20' lengths.
Azek isn't as rigid as wood. In fact, it bends like a wet noodle. Always nail it to a solid substrate. If the substrate isn't flat, the Azek will conform to the irregularities.
Azek-to-Azek joints can be glued with their PVC adhesive. It doesn't stink and is supposed to be non-toxic. You have about 10 minutes working time.
Azek PVC trim cuts like wood. Nailing it up is only slightly more difficult than wood -- this stuff is resilient and nails tend to "bounce" a little. For some reason, setting nails in Azek is really tough. Getting nails sunk far enough was nearly impossible.