两者都可以表示“至于”。as for 更倾向于比较性，两者有一定的对比。有时可以包含说话人的一种轻蔑、冷淡、不屑、甚至是厌恶之感;as to更倾向于客观陈述，谈话的内容大家都有所了解。
1.as for
1) 用以转换话题：在有前文的情况下as for总是出现在下文的句首,用来引出另外一方或者新的谈话内容,但与前文内容也有一定的联系,起到补充前文又突出后文的作用,使之与前文形成对照,译作“至于”.
例： ① You have a bed;as for him,he'll have to sleep on the floor.
你有一个床,对他来说,他只能睡在地板上。
② Much pasture land is underwater;and as for the grain, most of that has been ruined.
牧场是水下;至于谷物,大部分已经被毁了。
2)用以表现态度：as for还可以用来表示讲话人对某人或某物持有“轻蔑”或“冷淡”的态度,甚至有憎恶之感,讲话时要重读引出的词语并在其后稍作停顿,以示强调,口气上带有嘲讽意味,译作汉语的“至于……嘛”.
例：① As for you,I never want to see you here in my home again.
至于你,我再也不想看到你在我的家了。
② As for his songs,I suppose you've read the sarcastic reviews !
至于他的歌，我想你已经读过讽刺评论了吧!
2.as to
1)表示涉及某点：as to常放于句中,表示“关于……方面”、“有关……之事”,但为了突出要提及的人或事之时,也可将as to置于句首,以示强调.但只涉及内容,而不涉及讲话人的态度.
例：① His wife,an old teacher,has no complaint as to salary.
他的妻子,一个年老的老师,没有抱怨薪水。
② As to your ability to overfulfil the target,I never had the slightest doubt.
至于你超额完成目标的能力,我没有丝毫的怀疑。
2) 用以重提旧事：as to引出的内容都是前文曾经提到过的或者谈话对方都有所了解的,表示“说到”之义。
例： ① As to doing that,I haven't decided yet.
至于这样做,我还没有决定。
② As to the question you raised in your last letter,I think that it is unanswerable.
至于你在最后一封信提出的问题,我认为它是无法回答的。
3) 用于提出问题：as to必须位于句中,前面出现的大都是表达某种心理活动的动词,形容词或名词,其后引接出wh-clause或who-to-v结构,表示“在……的问题上”、“就……问题来讲”,所引出的问题都有很强的针对性.但有人认为这里的罄to显得多余,去之亦通.所以,有时也不必译出。
例： ① There is some doubt as to whether the proposal is practicable.
该提议是否可行是有一些怀疑。
② I enquired of the clerk as to which documents were needed.
我求问店员需要哪些文档。
4)引出做事的依据：as to还有“按照”、“根据”的含义,而as for则无此义.
例：① The shoes are correctly placed on the shelf as to size and colour.
鞋子是按照大小和颜色正确地放置在货架上。
② The items on the agenda are listed as to order of importance.
按照重要性顺序列出了议程项目
