Shadow if you are a better player - say upper 40%.
White Water if you are average or below for skill - lower 60%.

The more skilled players will start to feel like there's not really that much to do on WH20 - especially the lower playfield.
Just keep shooting the VUK, and you're pretty safe. The rest of the lower playfield is marginally utilized.

The less skilled players will usually not enjoy Shadow, because it can be brutal and they won't feel like they can accomplish much.

IMO Shadow is a much better game, but more people will probably prefer White Water as Shadow requires a higher skill level to "get to the fun part". This was my experience after owning both for many years.

If you focus on the VUK, you will also get the primary multiball - and the boulder awards are most of the modes in the game.
Wet Willies and Vacation Jackpot are great/fun goals, but most people are not going to get them very often (if at all).

The ramps may not be needed to qualify Final Battle - but who cares? The ramps are totally utilizes throughout normal game play: all the modes, Vengeance and Kahn MB. It seems like your main criteria is getting to the wizard mode, and you are ignoring the other 95% of the game play.

IMO balanced scoring and fun various modes are more important than only focusing on the Wizard mode. Since the vast majority of playing a game will not result in seeing/getting the wizard mode (at least in WH20 and Shadow), it's not as important as the rest of the game.

I totally disagree with this. If you set the game up right, Creature is not easy at all.
TIP - just make sure you set it up to play tough - it's one of the best 90's B/W games.