I was in Speyside last spring. I'm not able to tell you about anywhere else on the island. I dove with Manta but stayed elsewhere as Manta's reeort has been closed down.
Thank heaven's I'd just been in Maldives! The currents at Speyside were almost unbelievable and unfortunately the visibility was poor during my stay too. That said, it was exciting. On my last day, viz cleared right up and current moved to a leisurely drift. Amazing truly amazing for Caribbean diving. I loved it . . .until we surfaced!! OMG!! After such a lovely peaceful dive, we surfaced in the confluence of two opposing surface currents. for a few minutes there, I thought it was going to be an ironic way to die.
There was absolutely zilch for nightlife, nada!! However, that's at Speyside. I'm told that down south there's lots of restaurants and partying to be had.
I have stayed in Trinidad between flights 4 times and always stay at the Holiday Inn Express. It's not near much though apparently there's some kind of mall not too far away. The rooms are great!! I've been happy there each time with my only complaint being no restaurant/bar on site, only a breakfast room.
I may not be going through Trinidad to get to Grenada anymore so not sure I'll be back. As for Speyside itself, it was a once and done for me.
Grenada is a beautiful island. I'm definitely going to be there again and probably again and then again.