牛津高级词典第八版对clothes和dress的解释如下：

clothes: the things that you wear, such as trousers/pants, dresses and jackets.

              即衣服的统称，包括dress.

dress: a piece of women’s clothing that is made in one piece and covers the body down to the legs, sometimes reaching to below the knees, or to the ankles.

         女士的连衣裙。

因此，正确答案应该是：Dress is my favourite clothes.

在东湖路学校三（下）某班2017年4月初的一次英语家庭作业（Unit 3 练习2）中，有这样一道“连词成句”题：“is, dress, My, favourite, clothes”。老师所给的答案是：

My favourite clothes is dress.

我认为这个答案是错误的，因为 clothes 是复数名词，作主语时，谓语动词应该用复数。例如：Fine clothes make the man. （谚）人靠衣装。（摘自《外研社英汉多功能词典》2008年7月第1版）所以，正确的答案应该是：My favourite dress is clothes.

同意黎观点，只能以复数形式存在，作主语，谓语用复数

Dress is my favourite clothes.

These clothes are new.   
这些衣服是新的。

My clothes are cheap.   
我的衣服很便宜

Fine clothes make the man.   

马靠鞍装,人靠衣裳。

Many of the clothes come from the world's top fashion houses.  

这些服装中有很多出自世界顶级时装设计公司。

His work clothes, having become saturated with oil, had to be cleaned.  

他的工作服已经被油浸透，该洗洗了。

 He'd put his dirty laundry in the clothes basket.  

他会把自己的脏衣服扔进洗衣篮里。

 Clothes were thrown in the luggage in an untidy heap. 

衣服被乱糟糟地扔进旅行箱里。

同意黎老师的分析。原句中的 is 应改为 are。

clothes 是复数，作主语时应用复数谓语。又如：

Warm clothes are a must in the mountains. 在山里厚衣服是必不可少的。

Your clothes are often a reflection of your personality. 穿着常常反映出一个人的个性。

Sports clothes are not appropriate for a formal wedding. 运动服用于正式婚礼中是不适当的。

Summer clothes are invariably less kind to fuller figures. 体形较丰满的人穿夏装总是不那么好看。