What is the easiest language to build Windows services in?
Easiest in this case would be defined as least amount of code, and lowest point of entry into the language
I agree with everyone that has responded elsewhere, but I would say don't focus too much on the actual language, as long as you're working in the .NET framework, and there's a starter project for you, you're good to go. I've done several "Windows services" in the past, and developed them both in VB.NET and C#, with minimal code.
What I would recommend the OP to do is to learn how to build the installer package for it. Installing the service is as easy as executing "installutil.exe {drive}\path\to\file.exe", but when you have to do anything larger than deploying a "hello world" Windows service, it's good to know and understand how do deploy the service in a meaningful way.
Not to start a flame war, but I've "standardized" on using WiX for all my deployment packages, outside of doing old-school COM interop type stuff, since that's a brunt of work to get to install correctly. I'm anxious for the WiX team to develop the bootstrapper piece that allows you to put the prerequisites and the main msi into an EXE file which can be downloaded. They have it slated for 3.5, so I'll patiently wait, and use WinZip Self-Extracting executables for now.