IMHO, I think electric is better in both cases. Hard lines can vibrate and break. Stainless lines work well, but still require routing away from heat sources, clamping in places and can be expensive. Plastic lines (I think most gauges come with this) are very prone to rubbing and leaking.
Water temp is not a good item to use mechanical. Takes time for the temp to transfer up the tube from the engine to the gauge. Makes for slow reactions on the gauge. It's not like pressure, which is almost instant.
Also, any air in any of the lines will skew the indications.
Not really safe to run any mechanical gauges into the drivers compartment. Especially coolant.
Anyways, that's how I'd go. There's a good reason why very few mechanical gauges are used in aircraft.
I on the other hand prefer mechanical.
For the oil just use a copper feed instead of the factory plastic, it's only a few bucks.
Coolant doesn't go in the tube on a water gauge, although oil does go up for the oil.
I've always used autometer mechanical oil and water gauges, full sweep.
I don't trust sending units.