For you I would definitly go with Flamethrower.
Why? Well lets see how they're compared.
Flamethrower has a 90 base damage and 100% percent accuracy, and its learnt by leveling up your Typhlosion.
Fire Blast, even though it has 110 base damage, has 85% percent accuracy and you have to buy the TM for it for $5,500 in Golden Rod City Gamecorner. I don't know about you but I wouldn't want to spend that much time trying to get the money.
Now that we've decided for Flamethrower, let's look at your Typhlosion.
Held item: Choice Scarf
That is the moveset I would go with if I were you. I mainly choose dig because sumwun recommended it. But let's take a look at it anyway.
Dig has a base power of 80 damage and 100% accuracy in SoulSilver. Dig also takes two turns to use, you might want to be cautious about that. Dig is a TM that you can get for free in National Park, or if your to lazy to do that you could buy it at the Celadon City Department Store for $2,000.
(Which is still better than Fire Blast.)
Source: Pokemon Database
Hoped I helped!