what do people think the best angle to have your leg at when the crank is straight down?

say straight leg is 180. i find it comfy at like 160


I've heard a slight bend when the crank is down is ideal

That's pretty much the gist of it. You can raise it little by little to the point where you KNOW it's wrong (It'll hurt) Or you can ballpark it using the "slight bend" method. Remember you're working off the ball of the foot here not the arch

Remember too, that MTB leg extension is different than road bikes. On a MTB, you need more leg bend (seat needs to be a bit lower) in order to allow you to get off the saddle and behind it (over the rear wheel) if necessary on a steep downhill.

If your saddle is too high (too much leg extension), you are asking for an endo on a steep downhill if you don't leave yourself enough "leg" to get up, over and behind your saddle.

Certainly so. It's something you have to meet halfway on a trail rig. Up until I retired her from the trail I used to move the seatpost on my ol' Hardrock up and down depending on the terrain. I marked the trail spot (lower) with a piece of electrical tape and my road position was maybe a finger width higher.

Yep - QR seat post binders are one of the best thing to happen to MTB bikes. You get the best of both worlds (road and trail) with a quick adjustment.

The drawback being increased theft risk of course

I find it feels best for me (road bike commuting, clipless) if my leg is slightly bent when my foot is level, and I can just straighten the leg by dropping my heel.

What Ive been told is you want it so your knee is slightly angled, just barely. You want to have it pretty high, cept when going downhill you bring it all down.