Are SIPPs the Belle of the ball or ISAs' ugly sister?

When it comes to tax incentivised saving schemes personal pensions, in particular self-invested personal pensions (SIPPs), can seem to be portrayed as the ugly sister. In recent years issues such as failed esoteric investments, pension liberation and on going legislative changes, the reduction in lifetime allowance for example, have all contributed. On the other hand, ISAs, since their introduction in April 1999, cling on to their Cinderella status. So are there any lessons to be learned? The legislation in relation to ISAs compared to pensions legislation is relatively straightfor...