What type of micro roller should I use when applying finishes to wood.

Velour works best for laying down very thin coats, almost like you're spraying - perfect for cabinets. Great for Brushable White Enamel or even White Poly.
Micro-Fiber lays down a much heavier coat. Use this for full-bodied finishes such as General Finishes Milk Paints or primers. These load so much paint that they may leave a texture when using a high viscosity material like GF Milk Paint - just feather it out with a brush.
Nano Flock works best for applying thin coats of water based topcoats. They hold the product to be able to a do long strokes. These are also good for feathering out bubbles and lap marks.
Foam rollers work best for stains as they absorb a lot of product. This is helpful when staining large surfaces such as table tops. Do NOT use foam rollers with water-based topcoats - these cause it to aerate and produce bubbles.