Hermann, sorry, but you are completely 'wrong about your perception'. Both constructions are equally correct, and there's nothing 'bad' at all about the use of the gerund.

Triadhi Nugraha, here's the answer to your question:

If you are talking about an activity which you enjoy, you can use either of these constructions, and the meaning is exactly the same. It makes no difference whether it's your hobby or not. Generally, speakers of American English prefer the infinitive, while British English speakers prefer the gerund, but there is no difference at all in meaning. Personally, I would always the gerund in this context, but I've become accustomed to hearing the infinitive form more and more as global English becomes steadily more Americanised.

However....... in other situations there is a clear difference. If you say 'I like doing this', it means that the activity is enjoyable, as in 'I like playing the guitar' or 'I like swimming'.

But take a look at these sentences:

'I like to have full insurance cover whenever I go on holiday.'

'I like to have one day a week when I just drink green tea and miso soup.'

'I like to see my dentist once every four months.'

These activities are not enjoyable in themselves - obviously nobody actually enjoys paying insurance premiums, going without food or having a dental checkup. In each of these cases, we use the construction 'I like to do', not because the activity is pleasurable, but because it is a good thing to do - for financial, health or other reasons.

That's the difference - I hope it makes sense.

As for your secondary question, only the gerund form is natural in modern English. The infinitive form sounds stilted and old-fashioned.

Yes, I see how your Spanish-trained mind might resist the idea that  'I like swimming' means 'Me gusta nadar' - but I assure you it does! 

In fact, 'I like swimming' very rarely means 'Me gusta el nado'. It can, but only if the context is already established. And the only reason there is this ambiguity is because our word for 'el nado' happens to have an identical form to the gerund.  If I were you, I would forget about this meaning. It's pretty rare.

99.99% of the time, when an English speaker says 'I like swimming', they mean 'Me gusta nadar', just as 'I like playing guitar' means 'Me gusta tocar guitarra'. 

Triadhi - As Su.Ki. has explained, you should use the gerund in your examples. "Playing guitar is fun". "I love/like/dislike/hate playing guitar".

Paul - you mentioned a future event ("at first you did some stuff,but now you want to play guitar instead ...") so you should use the verb "want to", or its more polite form "would like to", e.g. "Now that I have finished my homework I would like to play my guitar" or "I have finished fixing the car and now I would like to wash my (very dirty) hands". I understand that it may be hard to hear the "would" in spoken English, as it is usually shortened to "I'd like to..." but it is important to use it as it has a very different meaning to "I like".  

Hermann - In your second question (addressed to Paul), you ask whether a sentence using like+gerund is more ambiguous than like+infinitive. No, it isn't. In most cases, verbs that express like/dislike - which include also e.g. "love", "hate", "prefer", "don't mind" - take the gerund. Here is an example of ambiguity: "I like football".  This sentence is grammatically correct, but the meaning is ambiguous. I have not said whether I like playing or watching football. "I like playing football", on the other hand, is not ambiguous. It is very clear. True, it does not suggest that I "know how to" play. I may play very badly, or I may play brilliantly, but whether I am good or bad at football, I do like playing it. 

As Su.Ki. mentioned, there are a few instances where an infinitive can be used - e.g. to express what you think of as a good habit but which is not necessarily enjoyable. But in general, I would suggest using the gerund.

I meant no offence to you, Hermann. You gave what appeared to be a tentative opinion, finishing with the phrase 'I may be wrong in my perception'.  All I did was confirm your suspicion.

Triadhi was happy with the explanation I gave him. If you choose to stick to your own beliefs in this matter, you are fully entitled to do so, and I sincerely apologise if I offended you in any way.

Your comments are very interesting, Sudeep.  Nonetheless, the flow is secondary when you talk about some other languages.  When you're used to German, for example, not Spanish, though... Spanish is like French and Portuguese; there's much poetry in them... German as well, if you read Goethe and others.  But in an everyday German, the flow dissapears.  Going back to English, you're right, the gerund is much smoother.

I hope eventually we have other interesting discussions.