oils/watercolour
Hi - in answer to your question - I think oils are easier.
You can change your mind entirely and cover things up, you can scratch back through it to reveal underlying layers, you can rub it off with a rag and get rid of it totally if you don't like it - or a palette knife.
You can glaze colours over others (dry) with no fear of ending up with mud!
Watercolour is wonderful and i love it too - but a little less forgiving or changeable.
When i work out in the landscape i mostly use oils as i can change quickly if a brilliant cloud formation appears or a flash of colour across the sea - I sometimes work in watercolour at home from these oil paintings - not the way round most people think of working but it suits me.
don't overdo the oil in the mix or you'll end up with sludge that takes forever to dry! I tend to paint with the paint alone and very little turps if any.
Oh intensity - you will need loads of white to get pale subtle colours.
Also the first colours put down can be very very thin, barely there, over a white background and they then have a luminosity that a pale colour mixed with white doesn't have.
As for intense vibrant colours - easy!!!!
I think somewhere i mentioned a book by Jeanne Dobie 'Making Color Sing'?? it is a very good book and refers to watercolour but is valid for anything.
Hope this is helpful.