よく使うintから文字列への変換Performance測定

計測コード

[MemoryDiagnoser, RankColumn]
public class ScoreBoard
{
	[Params(999999)]
	public int score;

	[Benchmark]
	public string Case1()
	{
		return "Score : " + score.ToString();
	}

	[Benchmark]
	public string Case2()
	{
		return "Score : " + score;
	}

	[Benchmark]
	public string Case3()
	{
		string scoreText = score.ToString();
		return string.Format("Score : {0}", scoreText);
	}

	[Benchmark]
	public string Case4()
	{
		return string.Format("Score : {0}", score);
	}

	[Benchmark]
	public string Case5()
	{
		return $"Score : {score}";
	}

	[Benchmark]
	public string Case6()
	{
		string scoreText = score.ToString();
		return $"Score : {scoreText}";
	}

	[Benchmark]
	public string Case7()
	{
		string scoreText = score.ToString();
		return ZString.Concat("Score : " + scoreText);
	}

	[Benchmark]
	public string Case8()
	{
		return ZString.Concat("Score : ", score);
	}

	[Benchmark]
	public string Case9()
	{
		string scoreText = score.ToString();
		return ZString.Format("Score : {0}", scoreText);
	}

	[Benchmark]
	public string Case10()
	{
		return ZString.Format("Score : {0}", score);
	}
}

結果

//BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
//Intel Core i5-9600K CPU 3.70GHz(Coffee Lake), 1 CPU, 6 logical and 6 physical cores
// [Host]     : .NET Framework 4.8 (4.8.4121.0), X64 RyuJIT
//  DefaultJob : .NET Framework 4.8 (4.8.4121.0), X64 RyuJIT

//| Method |  score |      Mean |    Error |   StdDev | Rank |  Gen 0 | Gen 1 | Gen 2 | Allocated |
//|------- |------- |----------:|---------:|---------:|-----:|-------:|------:|------:|----------:|
//|  Case1 | 999999 |  59.98 ns | 0.670 ns | 0.627 ns |    2 | 0.0204 |     - |     - |      96 B |
//|  Case2 | 999999 |  60.23 ns | 0.331 ns | 0.310 ns |    2 | 0.0204 |     - |     - |      96 B |
//|  Case3 | 999999 | 132.33 ns | 1.099 ns | 0.975 ns |    5 | 0.0203 |     - |     - |      96 B |
//|  Case4 | 999999 | 139.31 ns | 1.503 ns | 1.406 ns |    6 | 0.0253 |     - |     - |     120 B |
//|  Case5 | 999999 | 139.09 ns | 0.712 ns | 0.666 ns |    6 | 0.0253 |     - |     - |     120 B |
//|  Case6 | 999999 |  61.18 ns | 0.730 ns | 0.683 ns |    2 | 0.0204 |     - |     - |      96 B |
//|  Case7 | 999999 | 117.34 ns | 0.965 ns | 0.903 ns |    4 | 0.0323 |     - |     - |     152 B |
//|  Case8 | 999999 |  51.19 ns | 0.522 ns | 0.488 ns |    1 | 0.0119 |     - |     - |      56 B |
//|  Case9 | 999999 | 196.12 ns | 1.129 ns | 1.056 ns |    7 | 0.0203 |     - |     - |      96 B |
//| Case10 | 999999 | 108.29 ns | 0.723 ns | 0.676 ns |    3 | 0.0118 |     - |     - |      56 B |

ZStringが使えるならこれを使ったほうが一番パフォーマンスがいい。
無理なら
ToString() と +演算子の組み合わせ
ToString() と $ - 文字列補間がパフォーマンスが良い

文字列の変換数が増えるとパフォーマンスは変わってくるが...