As title really.

I'll be on a MTB following (roughly) the Tour du Mont Blanc. The walking TMB follows the Balcon Sud but to get up to it involve clambering up a load of ladders. One MTB route I've found online looks like it follows the Petit Balcon Nord for a while before swapping over the the Petit Balcon Sud around Le Lavancher. I'll be on either a HT or short travel FS with some luggage. I'm looking for the best route in terms of trail and scenery. I'll ride down most stuff but won't be looking for full-on DH tracks.

So….
~ is this the best route from Le Tour to Les Houches?
~ is there an easier way up to the Balcon Sud? (no ladders)
~ are there any even better routes?

No easy way with a bike onto the Balcon Sud, all paths will involve a good amount of carrying however the section past Lac Blanc has superb views and a lot of it is nice riding, you can get most of the way to Les Houches off road with some nice singletrack if you pick your path right after Plan Praz

The Petit Balcons combination is nice and involves quite a bit of up hill (that can be avoided on the road)nothing particularly technical but it can be busy with walkers, it can be done very quickly and you could get from Le Tour to Les Houches in ~30 minutes

Ta for the info.

Would the lift up to Flégère be an easier way up to the Balcon Sud? I'm trying to avoid lifts but I wouldn't object to taking one if it's worth it for the riding.

Or should I just stick to the 'petit' paths?

I'll keep my options open anyway – by this point I might just want a quick route back to Les Houches, a beer and a comfy bed!

For info, this is my route so far: http://www.mapmyrun.com/run/france/chamonix/954123765798617670

I would stay on the Petit Balcon Nord, at least as far as LeLavancher. The scenery is very nice, there are a couple of wee sharp climbs but they're worth the effort. The Petit Balcon Sud as shown on your link is mostly rideable but will involve gaining a fair bit of height towards Merlet. I would be tempted to stay on the Petit Balcon Sud side of the valley through to Les Praz, then take the lift and come down past the Floria cafe (get off and walk past the cafe if it is still open). As you say it depends how tired you are, you can always take the paths through Les Bois to Chamonix, have a pint and some food and then roll down the road.