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Only my opinion, but
Of these, I would go skywatcher.
and in particular, their flex tube dobsonian.
I believe it is the only one (of these) with Pyrex a mirror (I believe the others use BK7 glass in mirrors this size).
WHY:
Well reportedly, pyrex is superior due to:
"Telescopes using mirrors made of BK7 have more than twice the heat expansion than mirrors made of Pyrex. This means that in practice, a telescope with a Pyrex mirror provides us with a significantly better image during the heat expansion phase than a BK7."
Some of the other brands use Pyrex only in their mirrors of bigger than 10"
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