Same for me - CE was the cabin I saw myself never paying for but eventually did, completing my set of available cabins: UK, ET, WT, WTP, CW, First, CE.
One set that sticks in my mind now the 747 has been retired: I sat in every cabin of the 747 - WT, WTP-normal, WT-in-front-of-CW, CW-LD, CW-UD - except for F.
Another odd partial set for me is the BA's London airports - I have arrived and departed from LHR, LGW, but have only ever departed from LCY (although I have arrived on other airlines).