How to quickly check if two data transfer objects have equal properties in C#?

How about some reflection, perhaps using Expression.Compile() for performance? (note the static ctor here ensures we only compile it once per T):

using System;
using System.Linq.Expressions;

public class Report {
    public int Id { get; set; }
    public int ProjectId { get; set; }
    static void Main() {
        Report a = new Report { Id = 1, ProjectId = 13 },
            b = new Report { Id = 1, ProjectId = 13 },
            c = new Report { Id = 1, ProjectId = 12 };
        Console.WriteLine(PropertyCompare.Equal(a, b));
        Console.WriteLine(PropertyCompare.Equal(a, c));
    }
}
static class PropertyCompare {
    public static bool Equal<T>(T x, T y) {
        return Cache<T>.Compare(x, y);
    }
    static class Cache<T> {
        internal static readonly Func<T, T, bool> Compare;
        static Cache() {
            var props = typeof(T).GetProperties();
            if (props.Length == 0) {
                Compare = delegate { return true; };
                return;
            }
            var x = Expression.Parameter(typeof(T), "x");
            var y = Expression.Parameter(typeof(T), "y");

            Expression body = null;
            for (int i = 0; i < props.Length; i++) {
                var propEqual = Expression.Equal(
                    Expression.Property(x, props[i]),
                    Expression.Property(y, props[i]));
                if (body == null) {
                    body = propEqual;
                } else {
                    body = Expression.AndAlso(body, propEqual);
                }
            }
            Compare = Expression.Lambda<Func<T, T, bool>>(body, x, y)
                          .Compile();
        }
    }
}

Edit: updated to handle fields too:

static class MemberCompare
{
    public static bool Equal<T>(T x, T y)
    {
        return Cache<T>.Compare(x, y);
    }
    static class Cache<T>
    {
        internal static readonly Func<T, T, bool> Compare;
        static Cache()
        {
            var members = typeof(T).GetProperties(
                BindingFlags.Instance | BindingFlags.Public)
                .Cast<MemberInfo>().Concat(typeof(T).GetFields(
                BindingFlags.Instance | BindingFlags.Public)
                .Cast<MemberInfo>());
            var x = Expression.Parameter(typeof(T), "x");
            var y = Expression.Parameter(typeof(T), "y");

            Expression body = null;
            foreach(var member in members)
            {
                Expression memberEqual;
                switch (member.MemberType)
                {
                    case MemberTypes.Field:
                        memberEqual = Expression.Equal(
                            Expression.Field(x, (FieldInfo)member),
                            Expression.Field(y, (FieldInfo)member));
                        break;
                    case MemberTypes.Property:
                        memberEqual = Expression.Equal(
                            Expression.Property(x, (PropertyInfo)member),
                            Expression.Property(y, (PropertyInfo)member));
                        break;
                    default:
                        throw new NotSupportedException(
                            member.MemberType.ToString());
                }
                if (body == null)
                {
                    body = memberEqual;
                }
                else
                {
                    body = Expression.AndAlso(body, memberEqual);
                }
            }
            if (body == null)
            {
                Compare = delegate { return true; };
            }
            else
            {
                Compare = Expression.Lambda<Func<T, T, bool>>(body, x, y)
                              .Compile();
            }
        }
    }
}