What would be the ideal choice of spokes for enduro, all mtn or freeriding? would it be a double butted, triple butted or just single?
The best spoke is one that is light enough, strong enough to carry you, stays true through whatever riding you do, and doesn't cost too much.
To that end, the more butting on a spoke the thinner and lighter it is in the middle, but that adds to the expense.
You also need to consider whether you want normal brass nipples or aluminium ones which are lighter and cost more.
Other considerations for your wheel build might include spoke head washers, and whether the rim needs special nipples and/or washers.
Costs blow out quickly - you may only be paying 2 to 3 localdollars per spoke but 32 for the wheel and three for spares gives you $70-$105 just for spokes. Nipples may or may not be included so check that. Also see if a box of 50 is cheaper than buying 35 separately.
You can also make choices in colour (chrome/black/coloured+anodised/galvanised) and profile (bladed spokes for more aero) but realistically it doesn;t matter and weird/unusual choices will cost you more in the long run.
Do buy a new spoke tool if your old one is a bit sloppy. The right tool helps a lot and prevents rounding off.
We don't normally recommend products by name, but if you go into a LBS and buy spokes you'll probably be offered DT spokes, which are perfectly adequate. Check their website for comparisons, but notice that they don't have specific spokes for downhill vs uphill vs espatchio vs whatever kind of riding you want. A good wheel is a good wheel anywhere, and the tyre has more variation on the type of riding.
I'd bet a 29" MTB rim in a road bike, or a 700c road rim in a MTB would work perfectly well for either terrain.