It's an easy win for me. I wasn't alive for 1992 but even so statistically, 2020 beats the band by far. May 2020 was Dublin's sunniest month since July 1955 with 295.0 hours. May 1992 sun wasn't anything special with 204.0 hours whilst May 2018 was relatively sunny but not exceptionally so with 224.0 hours and comparable to May 2017 - which out of the two I prefer 2017. The first 10 days of May 2017 (minus the 6th) were great with clear easterly winds giving plenty of sunshine here, low humidity and non-hazy skies whilst I believe southeastern England had to content with cloud a lot.
Lockdown rubbish doesn't influence my opinion of how epic May 2020 was.
In terms of mean maximum temps, 2020 also beats the other 2. A mean max of 17.3C in 2020 as compared to 16.2C in 1992 and 16.9C in 2018.
Oh yeah and to round it off, only 9.3mm of rain in 2020 whilst 2018 had 19.1mm (also very dry) and 1992 had 39.5mm.
It's a full house for May 2020 here statistically.