To put them in order is cruel indeed. And you've missed out his real 9th symphony - Das Lied von der Erde. Oh well, I'll try with the numbered ones alone.
9 - powerful, disturbing, heartbreaking
10 - agonised, disturbed, the last movement always reduces me to tears
6 - 'Classical' in structure. Love the relentless marching of the 1st movement and the drama of the 4th (in which order do you think the middle two movements should be?)
7 - weird and wonderful. Underrated
2 - the last movement just transports you somewhere else
3 - HUGE, divine, satisfying
4 - his 'chamber' symphony, full of hidden depths
5 - a little overplayed, perhaps but the central scherzo is masterful
1 - again, overplayed. I like the original version (1889) with 'Blumine'. Makes sense of the rambling 4th movement
8 - beautiful moments - I just find the structure a little creaky
If I included 'Das Lied von der Erde', it would come between 3 and 4 on my list.
Edit to mephisto:
I think to ignore the Tenth (I realise you don't say you ignore it but you suggest it with words like 'bastardisation') is a mistake. I think what is most notable between the various 'completions' are the similarities rather than the differences (on the most part), which suggests to me (who hasn't seen the original sketches) that the symphony was in an advanced enough state to warrant such a 'completion'. I can't comment on the views of the Bernsteins, Boulezes, Haitinks, Kubelíks and Walters (I did work with Haitink once and, foolishly, forget to ask him about this!) but I think it was THEIR loss to ignore the Tenth. For whatever faults it may have, I would not want to be without it as it contains some of Mahler's most profound, heart-breaking and terrifying music.
Maybe we should have a question on the various performing versions out there?