Which is the best encryption mechanism?

Tripple DES is a bit outdated. (DES itself has been around since the sixties). A modern laptop probably has the computational power to break it. A better choice would be AES but I tend to use twofish because I like the name. Don’t know enough about the other to make a recomendation. Sorry.

What are you encrypting? Who needs to read it?

Credentials and data. Basically, everything between client and server.

I won’t be implementing the encryption personally… instead merely selecting from several built-in functions. Of those, the implementations provided of 3DES and RC4 meet my minimum requirements.

Sounds like a stream cypher would be more suitable so in that case, RC4.

How concerned are you about man-in-the-middle attacks and key exchange?

For this implementation, it’s all corporate intranet.

So attacks are possible, but not probable.

Then you’re probably best off with RC4.