Find out:
What are the charges on each pension...
What the range of investments are available for each pension...
What (read something like Tim Hayle's "Smarter Investing") you want your money to be invested in ...
(regardless of whether it's in a pension or an Isa or no wrapper at all)
My employer matches contributions up to a point and does it all via salary sacrifice. So I put masses of my salary into my work pension, then every so often I transfer most of that pension into my SIPP, which has much lower charges. In the work pension it's invested in a very low volatility fund as it's not going to be there long. In the SIPP I have the mix of investments I actually want (mainly low cost index tracker ETFs and investment trusts).
Like a lot of people I had 2 or 3 defined contribution work pensions but then sorted things all out about 5 or so years ago. By then I'd built up enough that x% (uncapped) taken out of my holdings every year was enough to make me sit up and see if I could reduce that!
Bear in mind that money goes into your pension tax free and only 3/4 of it gets taxed on the way out. If it's salary sacrifice even better as you don't pay NI on the sacrificed bit.
ISAs you've paid tax on all of the money already before it goes in, but don't pay tax on it when it comes out.
No Isa or pension wrapper at all - you pay tax on all of the money before you got your hands on it to invest it. You get some tax free allowances for dividends and for capital gains but beyond that have to pay tax on income & profit-upon-sale re your investments.
So saving for retirement (assuming you have other savings pots for emergencies / that new car etc) it often makes sense to max out pension contributions first, then (would be nice) anything surplus into an ISA up to (again nice) that limit.
But you can invest in pretty much anything in an ISA or pension wrapper - if not directly then indirectly, through the shares of an investment trust which can.
If your existing pensions don't offer a wide enough range of investments you find a SIP which does.