Best
This is the most ubiquitous; it's totally safe. I recommend it highly and so do the experts.
最普遍；最安全。我和专家们都极力推荐这个。

My Best
A little stilted. Etiquette consultant Lett likes it.
有点生硬。礼仪顾问莱特喜欢这个。

My best to you
Lett also likes this one. I think it's old-fashioned.
莱特也喜欢这个。我认为它过时了。

All Best
Harmless.
可以用。

All the best
This works too.
这个也可以。

Best Wishes
Seems too much like a greeting card but it's not bad.
看起来特别像贺卡，但是还不赖。

Bests
I know people who like this but I find it fussy. Why do you need the extra "s"?
我知道有人喜欢，但是我觉得它很繁琐。为什么你需要多余的“s”？

Best Regards
More formal than the ubiquitous "Best". I use this when I want a note of formality.
比最普遍的“Best”更正式。当我想要正式的写结尾时我会用这个。

Regards
Fine, anodyne, helpfully brief. I use this.
不错，稳重，简短。我用这个。

Rgds
I used to use this but stopped, because it's trying too hard to be abbreviated. Why not type three more letters? OK if you're sending it from your phone.
我过去常用这个但是现在没用了，缩写太过了点。为什么不多写几个字母？如果是用手机发邮件的话，这个OK 。

Warm Regards
I like this for a personal email to someone you don't know very well, or a business email that is meant as a thank-you.
我喜欢在给不是很了解的人发私人邮件时用这个，或在商业邮件里表达谢意。

Warmest Regards
As good as Warm Regards, with a touch of added heat.
跟Warm Regards一样好，且更增添了一丝温暖。

Warmest
I use this often for personal emails, especially if I'm close to someone but not in regular touch.
私人邮件中我常常用这个，尤其是当我跟某人比较熟但又不常联系时。

Warmly
This is a nice riff on the "warm" theme that can safely be used among colleagues.
这是一个关于 “warm” 主题很好的结尾，在同事之间使用很安全。