还是 asks, 或者 answers
甜的还是不甜的 offers a choice between two things, and 还是 is used only in a question. In a statement, "or" is 或者: 甜的或者不甜的都可以, either is fine by me. Using 还是 in a statement is the commonest mistake at this stage.
Xiaoyu is choosing bread, Chen Hao a cake and some milk. The assistant lets them help themselves from the fridge.
Xiaoyu
这个面包是今天的吗?
Zhè gè miànbāo shì jīntiān de ma ?
Is this bread today's?
The shop assistant
是,早上刚做好的。
Shì, zǎoshang gāng zuò hǎo de.
It is, made fresh this morning.
Xiaoyu
那我要两个。甜的还是不甜的好吃?
Nà wǒ yào liǎng gè. Tián de háishi bù tián de hǎochī ?
Then I will take two. Which is better, the sweet one or the plain one?
The shop assistant
不甜的,很多人买。
Bù tián de, hěn duō rén mǎi.
The plain one, a lot of people buy it.
Chen Hao
我要一个蛋糕,再要一瓶牛奶。
Wǒ yào yī gè dàngāo, zài yào yī píng niúnǎi.
I would like a cake, and a bottle of milk as well.
The shop assistant
牛奶在冰箱里,您自己拿。
Niúnǎi zài bīngxiāng lǐ, nín zìjǐ ná.
The milk is in the fridge, help yourself.
Chen Hao
好。蛋糕可以放两天吗?
Hǎo. Dàngāo kěyǐ fàng liǎng tiān ma ?
Right. Will the cake keep for two days?
The shop assistant
今天吃最好。
Jīntiān chī zuì hǎo.
It is best eaten today.
Xiaoyu
一共多少钱?
Yīgòng duōshao qián ?
How much is that altogether?
The shop assistant
二十六块,谢谢。
Èrshí liù kuài, xièxie.
Twenty-six yuan, thank you.
甜的还是不甜的 offers a choice between two things, and 还是 is used only in a question. In a statement, "or" is 或者: 甜的或者不甜的都可以, either is fine by me. Using 还是 in a statement is the commonest mistake at this stage.
甜的 means "the sweet one" without repeating 面包. Chinese puts the adjective, adds 的, and the noun disappears: 大的, 便宜的, 我的. It is the same particle as in 我的钱, and it is what makes a shop conversation so short once the goods have been named.
刚做好的面包 is bread that has just been made. 刚 goes in front of the verb and speaks only of the very recent past, minutes or hours. It is not to be confused with 刚才, which is a moment in time ("a while ago") and goes at the head of the sentence.