How to properly compare decimal values in C#?

Your code will work as expected. C# decimals are optimized to be very accurate at representing base 10 numbers, so if that's what you're comparing (money, ...), everything should be fine.

Here's a very clear explanation about the accuracy of decimals by Jon Skeet:

Difference between decimal, float and double in .NET?

I was investigating something similar, but with a precision instead of a margin of error and ended up writing some extensions for Float. This can easily be adapted for any type though. I've got a complicated series of comparisons and this makes it nice and readable.

/// <summary>
/// A set of extensions to allow the convenient comparison of float values based on a given precision.
/// </summary>
public static class FloatingPointExtensions
{
    /// <summary>
    /// Determines if the float value is less than or equal to the float parameter according to the defined precision.
    /// </summary>
    /// <param name="float1">The float1.</param>
    /// <param name="float2">The float2.</param>
    /// <param name="precision">The precision.  The number of digits after the decimal that will be considered when comparing.</param>
    /// <returns></returns>
    public static bool LessThan(this float float1, float float2, int precision)
    {
        return (System.Math.Round(float1 - float2, precision) < 0);
    }

    /// <summary>
    /// Determines if the float value is less than or equal to the float parameter according to the defined precision.
    /// </summary>
    /// <param name="float1">The float1.</param>
    /// <param name="float2">The float2.</param>
    /// <param name="precision">The precision.  The number of digits after the decimal that will be considered when comparing.</param>
    /// <returns></returns>
    public static bool LessThanOrEqualTo(this float float1, float float2, int precision)
    {
        return (System.Math.Round(float1 - float2, precision) <= 0);
    }

    /// <summary>
    /// Determines if the float value is greater than (>) the float parameter according to the defined precision.
    /// </summary>
    /// <param name="float1">The float1.</param>
    /// <param name="float2">The float2.</param>
    /// <param name="precision">The precision.  The number of digits after the decimal that will be considered when comparing.</param>
    /// <returns></returns>
    public static bool GreaterThan(this float float1, float float2, int precision)
    {
        return (System.Math.Round(float1 - float2, precision) > 0);
    }

    /// <summary>
    /// Determines if the float value is greater than or equal to (>=) the float parameter according to the defined precision.
    /// </summary>
    /// <param name="float1">The float1.</param>
    /// <param name="float2">The float2.</param>
    /// <param name="precision">The precision.  The number of digits after the decimal that will be considered when comparing.</param>
    /// <returns></returns>
    public static bool GreaterThanOrEqualTo(this float float1, float float2, int precision)
    {
        return (System.Math.Round(float1 - float2, precision) >= 0);
    }

    /// <summary>
    /// Determines if the float value is equal to (==) the float parameter according to the defined precision.
    /// </summary>
    /// <param name="float1">The float1.</param>
    /// <param name="float2">The float2.</param>
    /// <param name="precision">The precision.  The number of digits after the decimal that will be considered when comparing.</param>
    /// <returns></returns>
    public static bool AlmostEquals(this float float1, float float2, int precision)
    {
        return (System.Math.Round(float1 - float2, precision) == 0);
    } 
}