I would maybe mix your days up with 2 nights in the Mid-Upper Keys and then 3 nights in Key West. I don't think you can base yourself in just one area for the duration and expect to see it all. Key Largo to Key West is a 4 hr drive there and back.

John Pennekamp State Park in Key Largo is a must visit and well worth a day exploration (boat tours, kayaking and loads more activities). Aside from that, Key Largo is mainly geared towards fishing, but it is a lovely spot.

Key West is a lovely city and isn't at all seedy like some people describe it. Yes, there is a fairly lively bar scene along Duval Street and depending on your take of how to deal with rowdy and drunk Americans you will either love it or loathe it (we loved it). It's not just all about the evenings though, during the day you can visit Ernest Hemingways House (with the 6 toed cats), visit the Southenmost point of the USA, do a Old Town trolley tour around the whole city, jet ski in the Atlantic (not for the faint hearted), visit Mallory Square to see the street entertainers, or just wander around. It's a very walkable city.

We stayed in the Sheraton Beach Resort in Key Largo which is now the Hilton Key Largo and loved it. Sheraton obviously knew they were selling up because some of the rooms needed some renovating, but it was still a nice hotel and also had the only beach in the Keys which you can on the website below.

http://www.keylargoresort.com/index.cfm

In Key West we stayed at the Ocean Key Resort which frankly was outstanding but very expensive. Walkable to everywhere, we had a car but didn't use it for the whole 3 days and nights we were there. It had a lovely pier attached to it where we had a number of beers whilst watching the sun rise, it was truly magical.

http://www.oceankey.com/oceankey_home.aspx

Staying near the Upper Keys also gives you the options of doing an airboat ride near Homestead or Florida City. It's not quite the Everglades but it is as close as you can get without setting foot in there.

Keep us updated on your plans.

Hi, thanks for the info we are still busy looking at different areas.

Cheers, Colin.

We picked up the booklet at the tourist information in Orlando which contains coupons for all hotels in the state.
We stayed at the Washington inn just off Duval street in Key West for $39 a night.We stopped at Key Marathon on the way down but I really wished we had just gone to Key West for an extra night.

Thanks for that Jay, good idea

cmp,I have just noticed you are going in March.This is a very popular time for American students on their spring break.They can be a bit of a nightmare and I encountered them in Fort Lauderdale.One good thing is some hotels dont allow them to stay,so it would be worth asking when booking anywhere.