Didn't get to try Eight 5G nor Maxx.
Simba showed 5G from Buona Vista then LTE while going underground from Redhill. Connection slight hiccup for a few seconds before Tiong Bahru station then back on, onwards all the way into Raffles Place, continued connectivity into Red Line all the way to Yishun. Yes, Yishun.
Anyway, Simba works for me 98% from this year so far, so let's hope all goes well.
Having said that, my primary phone has Simba, with Maxx being the data provider most of the time. Will I switch completely later? Let's see...