Sorry OP, I don't want to confuse things for you!
There are huge benefits to saving in a pension rather than ISA :
1.Your employer will usually contribute, sometimes even matching additional contributions you make. This is worth maxing out: it's free money
2.Your tax is deferred. This is worthwhile even if you'll be in the same tax band in retirement, since you get the growth on the gross amount
3.You get to take some of your pension tax-free.
The only things that might put you off are:
1.You can't access it until a certain age - but sounds like you're in the clear anyway
2.You might find that the investment plan isn't what you want (which is what ozanj suggests)
3.You might be paying fees which aren't competitive (which does make a big difference)
If you're worried about negatives (2) then you have the option to open a sipp - which is similar to an ISA in that you choose your own funds, but still gives you all the tax advantages of a pension.
But the pension contribution from your employer is usually worth much more than that.
And if you're asking advice on returns, it sounds like you still need to do a bit more research before making your own investment fund choices.
My advice would be to find out whether your employer matches further contributions. If so, it might be worth increasing your pension even further (possibly using some of your ISA now instead). But get advice!