No advantages or disadvantages in game its self. If you like the story, and want a "happy" ending go with....
Bhelen below is the entire paragraph that is in the epilogue.
Waring contains spoilers for the paragon of her kind quest.
Siding with Bhelen and destroying the Anvil will cause Orzammar to come into a new age of prosperity at the expense of a dictatorship. Bhelen strengthens Orzammar's ties with the surface world. He also grants casteless greater rights and privileges in exchange for fighting the darkspawn. This policy allows Orzammar to reclaim lost territory, but it upsets the noble and warrior castes. After several failed assassination attempts, he dissolves the Assembly and rules alone.
Compare this to the harrowmont epilogue
If Harrowmont becomes king, he further isolates Orzammar from the surface world. Harrowmont will eventually die - suggested he could not handle dwarven political infighting anymore, or he was poisoned
"A gay Duncan is still far and away more awesome than most characters"-MetalMikemon Dourtweg is the greatest person on the mass effect 2 boards.
Harrowmont - Nice guy, trusted advisor, isolationist, weak support in the assembly
Bhelen - royal jackass, killed a brother and framed the other brother, seeks better connections with surface, strong assembly support, seeks to do away with the caste system(equal rights for all essentially)
In the end, even for a "good" character, it is technically better to side with Bhelen as in the epilogue it shows that he is better for Orzammar. But truthfully it is up to you and your preference.
"I'm Commander Shepard and thi-Assuming direct control." - Keldean
Harrowmont is the better guy, but Bhelen turns out to be a more efficient king (although he does turn the place into an absolute monarchy instead of a constitutional one, or however you would describe the relationship between the Assembly and the king).
The thing that gets me is that there is no real indication in-game that Bhelen is a better ruler. A few people state concerns that he's wimpy, but unless you're meta-gaming and aware of the epilogue, Bhelen is just a scumbag.
I tried to side with Bhelen once... but then the only evidence he finds to discredit Harrowmont is FORGED! I threw up my hands at that point.
just a little addition here, if you talk with bhelens second and get the letters that show harrowmont has been cheating his supporters and then take the letters to the shaper of memories, the shaper will reveal the letters are fake and by doing additional dialogue with the shaper you can find out that bhelen was asking around about a law that would give him full control over the warrior caste during wartime like saaaaaay helping you fight the darkspawn. the long and short is that if you played the dwarf noble origin, then you know bhelen is a snake whos only out for himself and i dont nominate snakes to be kings
5 seconds to takeoff 126.96.36.199 OH MY GOD THERES A FIRE IN HERE EVERYBODY RU BOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM big explosion, american tragedy, but life moves on
Harrowmont gets my vote. It seems silly to me, at least from a role-playing position, to base a decision on the epilogue when your character shouldn't be aware of the outcomes. If I'm playing a good guy, which I always do, then it seems quite odd and out of character to vote for Bhelen.
The only difference between peace and submission is the mercy of your enemy.
^^ Even if that snakes leads his whole race into a brighter future, with a stronger economy, equal rights and expansion of the dwarven lands?
Vs a goody two shoes traditionalist who plunges Dwarven society into dark ages....
But without meta-gaming, you honestly can't expect your Warden to know that. Given the information we have in Orzammar, there's no clear sign that Bhelen would be a better king, just a selfish, brutal tyrant. Which he still is, even if he does make some improvements. It's hard to justify picking him over Harrowmont in that case.
The only way I can justify it is if I'm a Dwarf Commoner, or possibly a Dwarf Noble who thinks keeping the Aeducan family on the throne is more important than kicking Bhelen's ass for his betrayal.