Well, pensions are the most tax-efficient way to save for the long term, so for your overall wealth increasing pension contributions is the winner. The disadvantage is not being able to access the money until age 55.
A couple of points on your situation. First of all if you retire early you will presumably have a pension shortfall due to a lower number of years of service completed. Not a problem, but in some years time you'll need to carefully look at the benefit statements provided to ensure you understand what you'll get based on a reduced service period.
Secondly on additional contributions. Certainly you should consider that, and due to the up-front tax saving it's the best long-term savings option. I would also look very carefully about the AVC offer from your existing provider. Following the Auto Enrolment rules a lot of the providers have had to cut fund charges (AMC/OCF and platform fees) to around 0.5 to 0.75%. However, if you look up SIPP providers on the Monevator website you will see that there are a number of online investment platforms that have flat-fee accounts and access to low-cost index trackers like Vanguard ones at 0.15% charges, with maybe £100 a year in flat fees. Once you have a reasonable SIPP value of around £40k or more the flat-fee option works out cheaper. In the short term probably doesn't matter to you, the AVCs can always be transferred to another provider later, but in the long term even what looks like a small difference of 0.25% a year in fees adds up to thousands of pounds in lost value.
In terms of pensions versus ISAs etc. what I suggest you do over the next few months is set up some simple spreadsheets to do some very simple modelling, for example estimate what position you would be in at age 50, 55, 60 if you continue with current pension contributions and have other savings, versus increasing your pension contributions a lot. You don't need to be an expert in spreadsheets, could just assume level salary and 5% investment returns to ignore inflation, see how much money you end up with in different pots at what age, and using the 4% rule how much income that would give you. Then adjust where you save your money and see what difference it makes. It should give you some idea as to how much non-pension money you could need to cover early retirement until AVC money available, regular pension available, state pension available. I suspect though, if you plan to make maximum use of the £15k ISA allowance each year, and then plan to increase pension contributions for any excess (unless you have a mortgage you need to pay down), you won't go too far wrong.