Looking for a 2 night stay on London. Have always liked Hyde park area any hotel suggest ions around $300 per night? Anyone stayed at Andaz ?

'Hyde Park' could mean anything from Queensway or Bayswater to Knightsbridge or South Kensington to Marble Arch. Essentially a huge swath of central London. Since you want to get to Southampton I personally would want to be nearer to Waterloo (or possibly Victoria) than either Hyde Park or Liverpool Street. But if you are willing to pay a high taxi fare to get to the train, you can stay anywhere.

(I'm assuming you'll have a fair amount of luggage)

I wouldn't stay near Liverpool Street unless you have business in the City. Hyde Park is a large area, as Janisj says.
The Arch is a good boutique hotel just north of Marble Arch.

decided to stay at St. Pancras---looks very interesting!

. . . And getting to Southampton how?

There is a shuttle I have read about that is a day trip to the port, visiting Stonehenge.