Unfortunately there is no "best deal" with top levels of safety. You need to decide how much risk you are willing to take. A low risk approach would be to invest in a fund that concentrates on government gilts. The returns will be low but the fund should be safe. A middle risk approach would be to invest in a fund that concentrates on larger UK companies. A high risk approach would be to invest in a fund that invests in recovery situations or emerging markets.
The risk is not just of the company that you invest with going bust but, to reduce that particular risk, I personally like the transparency of unit trust pensions and investment trust pensions. I also feel that risks are reduced if you deal direct rather than through a financial advisor. If you, for example, invest in a unit trust and the unit trust provider goes bust, you still are entitled to the full value of whatever your money was invested in.