I run 9 and 10 speed cassettes with double and triple cranksets on road and mtb bikes. IMO a 7 speed with a triple was enough and a lot cheaper to maintain. The only reason to even look at 9 or 10 speeds for a mtb is simply because there's no choice. As per Shimano's tech documents, Tourney, Altus, Acera and Alivio are NOT intended for anything except city riding and smooth off-road paths. And those are the only component groups that are available in anything other than 9 or 10 speed.

So aside from that your component selection should depend entirely on its intended use. Saint is the ONLY Shimano group targeted at downhill and freeride. SLX is targeted primarily at trail riding and all-mountain, Deore is the most flexible and can handle trekking, trail or cross country. Deore LX is intended for trekking only. Deore XT can be used for trekking, but will also handle trail and cross country extremely well. XTR is the only component group specifically designed for cross country racing, and although it performs great at trail riding and cross country, its NOT suitable for free ride or downhill and is overkill for trekking or city riding - unless you just like the 'bling' factor.