HIPER is the best one I have found. Not having been railroaded into HP calculators by the American education system, and thus not being very familiar with them, I've always found the HP clones a bit clunky on phones. But I still much prefer the RPN option.
The free version does have an ad banner, which I have to tolerate although I paid for it ages ago because this phone doesn't have Google play on it.
A unit-aware calculator is what I really crave, however, and I keep going back to Google for that which is pretty shameful. E.g. (1GWh/ 1 year)/2 km^2 in W/cm^2
Oh yes. Derp! No one really uses graphic calculators in UK schools, so they're all the same to me to me to be honest. A £10 Casio was all that was ever needed at school, and I didn't need one at university either. So I never got any kind of deep connection with any model in the way that some people seem to live and breathe their favourite models.
A sad side effect of this is few get suckered into accidentally learning to write software by trying to pay games in their maths lessons.
The free version does have an ad banner, which I have to tolerate although I paid for it ages ago because this phone doesn't have Google play on it.
A unit-aware calculator is what I really crave, however, and I keep going back to Google for that which is pretty shameful. E.g. (1GWh/ 1 year)/2 km^2 in W/cm^2