From Tristan's answer, and comments thereto, it seems there's a range of opinions. So here's my take...
1: I met John yesterday (we became acquainted/were introduced for the first time)
2: I met with John yesterday (we had a meeting/discussion by arrangement)
3: I met up with John yesterday (we came across one another unexpectedly)
The bracketed supplementaries are my default interpretations in the absence of any other context, but it's important to note that #1 (by far the most common form) can be used with all three senses. Also, not everyone will recognise my distinction between #2 and #3 (but neither would normally be used in the first time sense).
Thus I would unhesitatingly say that in OP's context, seen is the better verb.
Tom is the best expert ...
Assertion of a fact. Where there are agreed criteria then there's no need to hedge an statement.
Djokavic is the current number one male tennis player in the world
When criteria are less certain, or we ourselves are not sure of our facts, or we wish to be modest by appearing to be uncertain of our facts we may use I think
I think Djokavic is the best male tennis played of all time
I think that the population of the UK is 50 million (actually 65 million)
This formulation implies that we are open to correction and discussion
Adding would softens this further, emphasises that we are uncertain
I would think that the population of the UK is greater than 50 million
The I would have thought formulation is normally used in a context where some information has recently been given. Depending upon the context it may imply that we are actually contradicting the information, or that we are expressing surprised acceptance.
I think Tendulakar is the best batsman of all time
I would have thought Bradman had a better record
that was disagreeing, suggesting that by some criteria Bradman is better
The current UK population is 65 million
Oh, I would have thought it was only 50 million
but now I've changed my opinion (this implied but not said)
that was agreeing, I thought it was 50 million, but I accept your statement of 60 million is correct. We could just say
Oh, I thought it was only 50 million
With pretty much the same meaning, the slight difference being that the second case implies it was actively in my mind, whereas the would form could imply that I hadn't really formed a solid opinion until now, but I would probably have guessed 50 million.
As your comment indicates we are indeed into shades of meaning and idioms. In these cases the tone of voice will often differentiate the meaning.
I would have thought Bradman had a better record
Would probably said with a questioning or challenging tone and raised eyebrow.
Best Answer
I'm not a fan of Ngrams, so my answer is based on personal opinion and experience.
Although I suppose that the three phrases would be perfectly understood in context, if I were to use one of them I'd go for the first one (I have no clue) or for a modified version of the second (I don't have a clue or I haven't got a clue).
I wouldn't use the second phrase as it is because in negative sentences the verb have is normally used either in conjunction with got, thus being an auxiliary, or preceded by "don't"/"doesn't"/"didn't" as any other verb.
As for clueless, OALD states that it is an informal, disapproving adjective which means "very stupid; not able to understand or do something", which is a deviation from the meaning of the previous sentences.