个人体验：个人免费，美式英语语音合成质量比较高，系统提供了多种语音风格选择。

语音合成示例代码

static string speechKey = "6daa5e17bb9b4681aabdf3.。。。。。。"; 
static string speechRegion = "eastus2";

    async static Task Main(string[] args)
    {
        var speechConfig = SpeechConfig.FromSubscription(speechKey, speechRegion);
        speechConfig.SpeechSynthesisVoiceName = "en-US-JennyNeural";
        speechConfig.OutputFormat = OutputFormat.Simple;
        speechConfig.SetSpeechSynthesisOutputFormat(SpeechSynthesisOutputFormat.Audio16Khz128KBitRateMonoMp3);

        using (var speechSynthesizer = new SpeechSynthesizer(speechConfig))
        {
            string text = "Enter some text that you want to speak";

            var speechSynthesisResult = await speechSynthesizer.SpeakTextAsync(text);
            File.WriteAllBytes("aa.mp3", speechSynthesisResult.AudioData);
            Process.Start("explorer.exe","aa.mp3");
        }
    }

所有语音列表

        var speechConfig = SpeechConfig.FromSubscription(speechKey, speechRegion);
        var allVoices = new SpeechSynthesizer(speechConfig).GetVoicesAsync().Result.Voices.ToList();
        allVoices.ForEach(x =>
        {
            if (x.Locale == "en-US" && x.Gender == SynthesisVoiceGender.Male)
            {
                Console.WriteLine(x.Gender + "," + x.ShortName);
                if (x.StyleList.Count() > 1)
                {
                    Console.Write("\t");
                    foreach (var style in x.StyleList)
                    {
                        Console.Write(style + ",");
                    }
                    Console.WriteLine();
                }
            }
        });