Wire when you can. Much depend on what you want to achieve. Gentle bends can be done on older wood but good, tight bends must be done when the wood is still flexible. Also depends on species. Some have a rep for being brittle so best time to bend is when the trunk/branch is very young and flexible.
Avoid wiring and bending most species while they are actively growing. Bending in full growth more can separate bark from wood and kill the branch/trunk. Especially noticed in Junipers so I usually stick to bending Summer through winter and avoid Spring.
Also note that much bonsai shaping is dome by pruning. Much of what you have on pre bonsai will be chopped off at some stage. Pruning back to a side branch gives a much more natural bend than wire ever will. Pruning also gives taper where wiring rarely does.
I'm mostly use wire to make slight adjustments and pruning to actually form the basic structure but different growers use different techniques successfully.