Any advise on picking a resort that would offer private romantic coves as well as a fun lively beach party.

We have been to all the Sandals resort with the exception of Antigua.
I would try looking at Sandals Regency they have the Bluff suites which are romantic. Great resort for evening entertainment and fun beach games.
Also try the River suites at Sandals Negril,"beautiful."
Sandals Royal Bahamain,and Sandals Royal Carribean has a private island which you can go to for a little more private time.
If you have any specific ? about any resort feel free to email me.

What do you think of StLucia vs Negril?

Jamaica is a shorter flight and is a much better property. St Lucia has bad beaches and are usually red-flagged all the time.

We love Jamaica just returned from Sandals Negril in March.This was our 4th trip to this resort....it is a lovely resort but you have to fight for a beach chair. As far as evening entertainment it was ok...but not the best. Jamaica is a much shorter flight but if staying at Sandals Negril you only have that resort and Beaches exchange privelages and who wants kids if you want to be romantic.
Sandals Regency has exchange privelages with Sandals Grande and the Sandals Halcyon. We have been to all of them the Regency 3 times and never have we been red flagged the beach may be alittle choppy at times but we still swam and snorkled. We have been red flagged at Sandals Ocho Rios.
We love St.Lucia it is so green and lush a beautiful island. Any other ? feel free to ask.

Thanks for your advise. Is the golf resort,Regency, more stuffy than the Grand. We hope to see a party cruise and a fun pool/beach area. We have three kids and this is our anual big trip without them.

I would say its not meor stuffy...butthe Grande is more active with the water sports, tubing,horseback ridding on the beach.You can visit the other 2 Sandals while staying at any of them.