Why not just use US Intl, and use ALT GR to produce á, é, í, ó, ú and ñ, along with æ, ø and å?

I have a strange ISO/ANSI US keyboard, with an ANSI left shift and an ISO enter key.

I didn't know about the US intl layout when I decided to make the switch, and I don't know if it's worth to learn it now.

I used to switch between US and DK layouts, it's just so much easier to just have one layout. In my opinion, learning US Intl is worth it. Besides, it's pretty predictable for Spanish characters: á = altgr+a, é = altgr+e and so on.

Yeah it's great for Spanish. But I found that knowing (and using) native layout is more valuable to me because when I need to type on someone else's keyboard I'm not lost and can still touch type. If you never need to do this US international is indeed superior layout.

Trying to remember more than two layouts becomes confusing very fast. AZERTY and QWERZ are the two worst ones, fortunately I never need to use those.

The British/Irish ISO layouts are reasonable. They are very close to the US layout, but gain the additional key.

I don’t think UK/ISO and US are close? Especially backquote between LShift and Z feels awkward if you’re used to ANSI.

These keys are in different positions: "@#~\|

These keys are present on the UK keyboard, but not the US: £¬

Compared to every other common ISO keyboard layout, ISO UK and ANSI are very similar. For non-programmers, ", @ and (nowadays) # are the ones that matter. For a programmer used to an ISO keyboard, the UK layout may well be a better choice than the US ANSI one. (US ISO would be a good choice, but the extra key seems to duplicate symbols already present on the layout).