IME ex-AMS is great for reasons outlined elsewhere. A similar fare seems to be available for most of the year, via LIS too. If you have reasonable access to LHR, judicious planning can ensure worry-free travel with the l/h flights starting and finishing in London, sleeping at home before and after:

outbound
Day 1: AMS-LHR (having back-to-backed or spent a <24 hour stay in NL)
Day 2: LHR-CPT, ensuring that this flight is <24 hours from the AMS flight

on the return:
Day 1: CPT-LHR arriving Day 2
Day 3: LHR-AMS ensuring that this flight is <24 hours from the inbound, though longer connections usually available at modest extra cost

I have b2b'ed using LIS, DUB, VIE, MIL using this timing; AMS wins for me because of the short connecting flights (can also use LCY or LGW) and the convenience of sleeping at home on the way in both directions.