Except for a very thin layer of soil in direct contact with the mulch there is no appreciable effect on soil pH. The choice of what you use really comes down to appearance, cost, ease of spreading and longevity. Nuggets are larger and will therefore last longer before breaking down. The mulch is finer, easier to spread and usually cheaper. All this applies to mulches spread on the surface. If you're using the mulch to incorporate into the soil to increase water holding properties and aeration, conifer bark mulch would be the best choice.

I would go with mulch over nuggets. I bought some mini-nuggets which are smaller than nuggets but bigger vs mulch. The mini-nuggets were 1-2" in size. I didn't like the look of the mini-nuggets so I will stick with mulch.

"just learned that I should be using pine or cedar based mulch."

I guess my rhodies and azaleas aren't reading the same info. ;>)

Seriously, though, as long as you aren't using hickory or Juglans (walnut and butternut), I don't have any idea why softwood would be an improvement over hardwood mulch. I use shredded hardwood because that's what is available to me low cost, and my Rhododendrons are just fine. Any shredded bark or natural wood based mulch will help retain moisture and slowly break down to add organic matter to the soil. Neither will appreciably change soil pH since that is pretty much determined by inorganic matter. So it's all good as far as I am concerned.

Thanks everyone! I'll stick w the hardwood mulch I've gotten over the years. It's very nice and cheaper too!