Do you have any more details about the oils, such as their viscosity, API rating and any other specs.
The HX5 is a mineral oil, the HX7 is a semi-synthetic, and the Ultra is a full synthetic.
My HX5 is a 15w40 mineral oil that is API SN and ACEA A3/B3. I think it's a good mineral oil for warm climates.
We also get a HX3 mineral oil that is 20W-50 and API SL. I would mostly avoid this old style oil with most modern or semi-modern cars, unless oil consumption was a problem.
Without having any more details, for your N16 and S13, I would run the HX7 in both of these cars. For me they are better oils than the HX5, but less money than the Ultra. A nice sweet spot in the range.
If the S13 had a Turbo or money was no problem, then I would happily use the Ultra. If I needed to save money, a SN rated mineral oil would be fine.