Golf Captain Hi,
I was in Seletar with a BBJ last year and we used Universal.I was extremely impressed with their service. We had to off load pax at Changi first (their choice) and Universal were there to meet us and then in Seletar when we re-positioned.
They were very helpful, curteous, and pretty well thought of everything (even a cold beer when we had put the aeroplane to bed!!!)
No idea about maintenance.
No experience of Jet Aviation there but got the impression that both FBO`s were keen for business.