I'm about to buy one of these two guitars. I've never played a Larrivee but I have the Martin. I strictly finger pick and I want a smaller instrument. Now, I'm playing a Martin D15 spruce/rosewood. I think the trebles are harsh and want to tone things down.However, some Martin Hogs are pretty dull and you don't know what you're getting when you order on-line. So how about the Larrivee?

I have been in a similar situation. I was able to try the OOO-15s extensively  - great guitar - but then bought OM-03MT online untried. It was in fact the lack of body binding on the Martin that did it for me as I am a bit clumsy.  I never regretted the choice - nothing harsh about the Larri, very sweet, but you can get all sorts of woody and blues noises out of it.  The Martin does feel a bit smaller though with 12 frets to body and a narrower upper bout than an OM size (except a Lakewood M series). Hope this helps. Either way you will have a good guitar, but I think the OM is better value. 

True some Martin hogs can sound dull, but in the 000-15s, you can find over 50 reviews online it is unanimously loved by its owners.

I've got both these guitars with the exception that my OM-03MT is a Forum I 12-fret guitar.  My 000-15s is sapele.  I love both guitars.  They both sound amazing and are my 2 favorite guitars that I ever owned.  I don't think you can go wrong with either one.  If I had to choose, I would choose the 000-15s because it's a 12-fret design.  That gives the guitar added volume and more bass.  Also, the slot head is awesome and I actually love the fact that the 000 has no binding, it's pure simplicity is it's charm.  A couple things though.  The tuners on the 000 are really cheap and destroy the slot head vibe with their modern closed back look.   I put these Waverly's on mine but it's over two hundred bucks to buy and have a luthier install.  You also need to order 12 bushings with them for the conversion.  Don't do it yourself because removing the old bushings can be tricky and an inexperienced hand can leave you with cracks in your slot head and a voided warranty unless you are a certified professional luthier.  Both the Larrivee and the Martin will sound better with an upgraded bone saddle, another 85 bucks to buy and have a luthier fit and also do a set up.   I don't think you can go wrong with either guitar.  They will both be great.  If you like playing blues, the 12-fret is nice too because you can just slide up the neck as far as you can and you end up on the 12th fret, great for open tunings.
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Ditto what Bluesman67 said. Either would be a good choice but I would upgrade the tuners and add a bone saddle right out of the gate on either guitar. The extra money will give you quality, tone and eye appeal.

Check out the current issue of Acoustic Guitar for the review on the Martin 000-15. It's not exactly the same as the slot head but I have played a number of nice 15 series Martins. I would give the Larrivee a slight edge on workmanship and I love the maple binding on my two but the Martins I have played against them on a couple of occasions sounded a little better (to my ear). FWIW, Trinity Guitars has an OM-03MT (South American Mahogany) in stock and is offering a free bone saddle. Shoot him an e-mail.

http://www.trinityguitars.com/steelstr/larrivee/graphics/om03mhmt/_C100901.jpg

Seems like this thread topic gets recycled.  So here's my rehash:

I owned the L-03MT and later the 000-15S (all hog, no wings).  Both are long gone.  I've played a few OM-03MT's and preferred the L version.  But overall the Martin was the best sounding of the bunch, maybe due to the 12-fret design.  The Larrivee sounded better with Tusq saddle while the Martin was best with bone saddle and ebony pins, all IMHO.  The Martin should have better resale, brand recognition and all.

If I was in the market for an all-hog guitar I would have ordered the LS-03MT as a sort of best of all worlds Larrivee hog-top.  But I have played a sapele 000-15S and thought it sounded a little better than my mahogany version. 

Enjoy the chase.

I think they are somewhat different guitars in design, though both very good.

I haven't heard the OM-03MT, but I have a Martin 000-15 and have played a couple 000-15S.  I think the standard 000-15 is a more direct comparison, in terms of body size/volume, but the bracing, finish, and other details differ; I think you can expect to get the "Martin sound" with the Martin, and vice versa.  I have heard a few 00015 guitars that sounded fantastic, and some that were more dark and quiet. 

The 12-fret 00015S has a larger body, and the bridge is in a different relative position on the top, and it should sound a bit different from a 14-fret OM as a result.  I have played one I thought was really stellar, and another that was just OK.  The Larrivee would have nicer appointments, whereas the Martin has the traditional, vintage thing going for it.