There is a temptation to buy multiple contracts from different companies. Avoid this unless contributing at least 100pm to each, as policy charges on small premiums can be significant. Contracts themselves vary a lot. A contract that is good for a long term high premium case may not be suitable for a short term one. Seek independent advice.
Performance is the great red herring.
Arguments that expensive charges are compensated for by good performance are sophist, as the charges are predictable, the performance is not. For the record the analysis of contract charges and performance is my business, an area in which I am one of very few UK experts who do not work for an insurance company. I invented the Pensions Analyser package used by many IFAs and some pension providers.