I think the lack of opinions given here is because the mechanicum players are all sensitive to just how personal your force ends up being - so I'd say have a look at the taghmata
hq options as they can be the basis for your forces functionality.
The archimandrite gives all vehicles
IWND for a vehicle heavy list, the lachrimallus allows for a highly amusing returning tech-thrall unit feature and benefits from tech-preist auxilia units dotted around in triaros.
And then of course there's my chosen clan, the Ordo Reductor - we have a bunch of restrictions, but also some nice benefits (walkers in ruin) and a couple of exclusive artillery units.
Have a look at the
hq options in the taghmata list and see if any army ideas jump out at you - if you have any Ordo Reductor based questions, i'll be happy to give an opinion!