Informal:
* 我在这儿待了好久了 (wǒ zài zhè'er dài le hǎo jiǔ le): This is the most common and informal way to say it. It literally translates to "I've been here for a long time".
* 我在这儿待了一会儿 (wǒ zài zhè'er dài le yī huì'er): This means "I've been here for a while" and is slightly more formal than the previous option.
Formal:
* 我在这儿已经待了一段时间 (wǒ zài zhè'er yǐjīng dài le yī duàn shíjiān): This is a more formal way to say "I've been here for a while". It literally translates to "I have been here for a period of time."
* 我在这儿已经待了很久了 (wǒ zài zhè'er yǐjīng dài le hěn jiǔ le): This is the most formal option, meaning "I have been here for a long time".
Example sentences:
* 我在这儿待了好久了，你还没来吗？(wǒ zài zhè'er dài le hǎo jiǔ le, nǐ hái méi lái ma?) - I've been here for a while, haven't you come yet?
* 我在这儿待了一会儿，就看到了你。(wǒ zài zhè'er dài le yī huì'er, jiù kàn dào le nǐ.) - I was here for a while, and then I saw you.
* 我在这儿已经待了一段时间，感觉就像回到了家。(wǒ zài zhè'er yǐjīng dài le yī duàn shíjiān, gǎnjué jiù xiàng huí dào le jiā.) - I've been here for a while, it feels like home.
Remember to choose the appropriate phrase depending on the context and the person you are talking to.