Are ISAs better for low or higher rate taxpayers?

Alexland

You each have a £20k per tax year ISA allowance so I would just split the £30k between cash ISAs paying a good rate and not give it any further thought other than to check the rate remains competitive. Once the money is in an ISA wrapper it doesn't matter what tax rate you are in. If you wanted to get a little bit extra return then I guess you could put some of the money into unwrapped regular savers etc that might pay a higher rate.

LL_USS

When/if ISA and LISA rates are (much) lower than those of other saving accounts, I put my savings into high-rate saving accounts just enough for the interest yielded that year to be lower than my personal allowance, then just before the end of that financial year I move the money from other saving accounts to ISA/LISA to use up my ISA/LISA allowance in time. For e.g. I am using Virgin regular saving with 10% rate but will use that saving plus interest to form a part of my ISA next year (can't take out earlier as it's one year fixed). Natwest regular saving with lower rate 6% but can be taken out any time, so I'll withdraw that to top up and use the rest of my ISA allowance at the end of this March.

It makes a difference for higher tax rate person to put the money in standard saving accounts if you need to choose between you two as you two have different personal allowances on interests earned outside of ISA/LISA. But once the money is in ISA/LISA it makes no difference whether it's in yours or your wife's, both will be taxed 0 on interests. I'd put 15K in each ISA between you two.