I feel like I can answer this question better. 覺得 - I think that, I feel that, I feel, It is my opinion that 我覺得他很聰明 - I think that he is really clever 我覺得很無聊啊 - I'm bored! 我覺得拉托維亞很漂亮 - I think that Latvia is a really beautiful county 我覺得很累喔 - I'm really tired 想 - I think (but this usually means "want") 我想應該是吧 - Yeah, I think it should be like that 認爲 - I believe that, it is my opinion that 我認爲學習漢字不是很難，只是需要花很多時間才能學好而已 - I believe that studying Chinese characters isn't difficult, you just need to spend a lot of time to master them 我不認爲考試重要 - I don't believe exams are important 我認爲看書是一個很不錯學習外語的方式 - I believe reading is a great way to learn foreign languages 以爲 - I thought that it was like this, but it turn(s/ed) out I am wrong 我以爲他是法國人 - I thought he was French (but actually he's not) 去香港之前，我以爲香港只是一個大銀行，沒有什麽好看的，不過我錯了！香港的景色很好啊！ Before going to Hong Kong, I thought that it was just a big bank with anything that looked nice, but I was wrong! The scenery in Hong Kong is amazing!

'认为" ,which is more formal and sure ,and have some evidences to support his idea. '想,觉得 ”is a oral language ,just expressing personal view ,maybe is not true, and don't have strong objective evidence to support it.

Actually there is no difference to use these two words, but the meaning is not the same. “想” signifies subjectif wishes. You can translate this word "want to" in english. For example : 我想学中文。I want to learn Chinese. 我想吃饭。I want to eat. ”觉得“signifies emotions. You can translate ”think，feel“。For example : 我觉得中文很简单。I think Chinese is very easy. 我觉得这个问题很复杂。I think this question is complicated. I hope my explication will help you.

These three words have quite many usages. I will just explain the differeces when they are used to express an opinion. On This Premise When you make a sensory evaluation such as feeling cold/tired, you use 觉得, it is always followed by an adjective. Otherwise incorrect. e.g. 我觉得很冷/很无聊。 When you want to do sth, you use想, it is always followed by a verb. Otherwise incorrect. e.g 我想睡觉/看书。 In other cases, they are basically the same, and always followed by a complete sentence. Hope that helps. Note. Please notice the premise.

觉得和认为很好解释。但”想“这个词非常复杂，并不是一两句话能说的清的。