Bonsai wire

I have been researching aluminium wire and it seems to be easier on the wallet. What type of wire do you guys use and why?

I use both, depending on multiple factors, but mostly copper.
To begin, as I'm sure you've already researched, copper holds shape better with only ~ half the diameter as aluminum. Also, I work for a lighting manufacturer, so scrap copper wire is readily available on the cheap, whereas aluminum wire has to be ordered.
Aluminum, to some degree, is forgiving, so a poor wiring job (especially when first starting bonsai) can be adjusted much quicker than if it's copper.
All wire digs in if you leave it too long. I like copper on my junipers and pines as they're slow(er) growers and don't thicken as quickly as a deciduous. I prefer aluminum, if I have it, on deciduous, because I'm going to be cutting it off within a season. The thicker wire doesn't bite into the growing branch as sharply as thinner wire, and therefore the scar is lessened if I haven't caught it in time.
For the most part, the type of wire isn't going to be so important, as it's just used to train your tree. Most trees with loads of wire aren't ready to show anyway, so whatever alloy and color works for you. However, it is acceptable to have wire on show trees, and copper is preferred, but anodized aluminum is gaining more acceptance.

Funnily, this website suggests that you should use aluminium for deciduous species and copper for conifers and pines, although I'm not sure if there is a reason other than the growth rate issue that brkirkland22 brought up.
I think it does come down to personal preference in the end, maybe you could try using both then deciding your favourite.

Copper wire is expensive and whilst it may work well, it is no better than aluminium in use. Both do the same job equally well. The difference is the cost. Copper wire is twice the price.

m5eaygeoff wrote: Copper wire is expensive and whilst it may work well, it is no better than aluminium in use. Both do the same job equally well. The difference is the cost. Copper wire is twice the price.

And because it holds more strongly you can use wire half the thickness, which evens out the costs agains :)I find that a .6mm copper wire holds better than the 1mm aluminiium for styling the very thin stuff on juniper. Aluminium stays more flexable in the end than copper.

This is one of the the main reasons for using copper; Once your tree gets to a certain level it gets hard to get a wire in between branches; You want to use the thinnest wire possible. Which is copper.

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Thank you guys, that is so helpful!