Mountain Biking - Alt Handlebars, Riding Position advice needed

Hi
New to mountain biking, comeing from a road/commuter background.
Building up a mountain bike.

I'm looking for advice on the different positions/riding positure used with different handlebar styles.
At the moment, I am considering two handlebar styles: dirt drops, or flatbars with bar ends

dirt drops, 2 main positions, hoods vs drops

flatbar w ends, 2 main positions flats vs ends

both styles have a relaxed location - hoods, flats
and an aggressive location - drops, ends
however, with the dirt drops, change in posture is mainly vertical -up/down
while with the flatbar w ends, change in posture is mainly horizonal -back/forward

also, the ability to shift is different for each style
with dirt drops, (barcon shifters) shifting is convenient from the aggressive location -drops
with flatbars, shifting is convenient from the relaxed location -flats

So, being new to mtb, I'm not sure what kinds of riding positions are going to be used and for what purposes. Is it more useful for the change in position to be vertical, or horizontal?
Is it more useful to shift quickly from an aggressive or relaxed position?
any suggestions?
Thanks

I think that few people use dirt drops on really technical stuff, they are more common on fireroads and double track. I sure wouldn't want them.

I don't use bar-ends on my flatbars on tech trails, either, but I've seen it. I would bet those guys occasionally hook a bar end and go down but maybe they ride a lot on gravel or even the road and need them.

So, what kind of MTBing are you going to be doing? If it involves a lot of rocks, roots, climbs and jumps I would suggest you start with flatbars. To get aggressive on them, just use a longer stem and/or bend forward with a lot of elbow bend. You will see me doing this every time I go into a headwind on a flat, fast section of trail.

You may want to look into Luv Handles By Groovy Cycle Works I run them on a couple of bikes amd wont run anything else now on my MTB's
http://www.groovycycleworks.com/Pages/LuvHandles.aspx

Another option is controls on barends. Get some thumbshifters and...

http://farm6.staticflickr.com/5270/5676124568_28a4a03d2e_b.jpg (http://www.flickr.com/photos/lesterofpuppets/5676124568/)
Controls on the barends (http://www.flickr.com/photos/lesterofpuppets/5676124568/) by Lester.L. (http://www.flickr.com/people/lesterofpuppets/), on Flickr

I'm not real sure what the issue is that the OP is trying to solve.

I would just ride flatbars for a while. Yes, they are different than drop handlebars, and I feel that each of them are optimal for their typical usage. I wouldn't take drops into the woods, but you can, and I wouldn't choose flatbars on a 30+ mile gravel or pavement ride, but you can.

Another option is controls on barends. Get some thumbshifters and...

http://farm6.staticflickr.com/5270/5676124568_28a4a03d2e_b.jpg (http://www.flickr.com/photos/lesterofpuppets/5676124568/)
Controls on the barends (http://www.flickr.com/photos/lesterofpuppets/5676124568/) by Lester.L. (http://www.flickr.com/people/lesterofpuppets/), on Flickr

Funny you should mention that, though i didn't say it initially for fear of scaring off people; my flatbar w bar ends option would have inserted TT reverse brake levers into the tips of the bar ends; and I would spend most of my time on those. Essentialy pursuit bar/bullhorns from roadie territory.

What kind of MTBing ? No idea, i'm new to mtb, you mean there's more than one kind?
The kind that newbies start with I guess.

Why not plain flatbars like comes standard everywhere?
-the normal bar trend seems to sweep about 6degrees, this hurts my wrists; makes me reluctant to just go with the flow
-I'm building from the frame up, there are no constrained presets

If you want more sweep, I'd look at the link in post #3-- LuvHandles.

But yes, there are many different kinds of trails.