I recently did a lot of research on all the different types of 4WD on the 4Runner. From what you mentioned it seems the SR5 will best suit your needs. Here’s why.
The SR5 has the following types of gear settings
2WD
H4F (High 4x4 Free)
H4L (High 4x4 Locked)
L4L (Low 4x4 Locked)
The H4F is essentially a limited AWD mode. I say limited because it recommended only to be used when driving 55 mph or less. This is very handy for snow, heavy rain and moderate off-roading. You can drive with this on all the time if you wish as long as you don’t go over 55 mph with slight reduction in fuel economy.
The H4L locks the center differential. This turns it into a true 4WD for medium off-roading or where you are driving on snow only. It provides better traction because all your wheels are turning at the same speed. The drawback is that your turning radius will be reduced. Do not drive on pavement because turning can cause the gears to bind which can damage them. This link provides a better explanation.
YouTube
The L4L provide more torque for heavy off-roading albite at lower speeds
The TRD has a different type transfer case. As a result it does not have a H4F or limited All Wheel Drive capability. It only has H2 (2WD), H4 (4WD) and L4 (4WD). But in addition to this is has a “Crawl” and “Multi Terrain” select feature that gives it heavy off-road and rock crawling capabilities.
I have a TRD Pro and I love it. However, I use to have a Isuzu Trooper that had a selectable AWD function. I do miss that capability when driving in heavy rain or mix snow and pavement driving