NE1 using Mobil 1 5w-20?

It won't make that big a difference in Hawaii, use 0w or 5w, it would be the same in your climate.

I find using mobil 1 oil burns quite easily in my Priis. When I switched to Pennzoil Platinum, the oil burn/usage reduced. Not sure why

 

I'd never use a non-synthetic. Based on my past experience, it's the difference between "some" engine-wear and no engine-wear. Several of my previous vehicles have gone over 250,000 miles using it, and I've often gone more than 20,000 miles between oil changes, with no apparent bad effects.

I can see why Toyota recommends it.

 

Although both a synthetic oils, both are not made of the same synthetic formula. All oil companies have their own special formula for success. I believe the mobil 1 formula is their great advertising

 

How cheap was it? I just paid 22.99 for a 5 qt jug of mobil one.

 

This sounds like a Mobil 1 advertisement

 

It's a bit like asking yourself: "Do I want engine-wear, or no engine-wear."

 

I experience no engine wear on my cars too. When they are parked

 

Not bad at all when you stretch it to 20k.

 

Walmart has Mobil-1 for $22.xx 5-qts jug, just got some 0W-40 (not for the Prius) but that is really low price.
As far as OP I see no issue with 5W-20 in Hawaii.

As far as who has the best synthetic, I do not know. Most say the Toyota brand is made to quite high specs.
You can look for ACEA A1/B1 A5/B5 rating but last time I looked, I do not think many if any USA 20 weights have that rating (30 weights for Gen2 we can get ACEA A1/B1 A5/B5 on the label).