Server thoughts using Asnyc vs Sync sockets

Question

Hi all,
just thought id ask you guys for your thoughts on something i'm looking into doing.

Basically looking to develop a Server that will accept TCP connections. The clients will not be connected constantly, i.e the clients open connection, send data to the server, the server will send back ack, nak or some data and then the client closes.

The amount of clients the server will have to service will be around 1000-2000, but i would like the confidence of knowing it would work with more :-). 

The connections from the clients will be totally random with regards to time thus, in theory there is a possibility that the server could get hit with 100s of requests at any instance in time.

So my question is what do you guys think the best route to take is for the server side sockets is ? Async ? Sync ?

Also another thing i should mention is the data the server receives will need to be pushed into a SQL database.

Look forward to any comments you have :-)