I would say Life Orb
Typholosion itself isn't very bulky, but it can tank at least one or two hits, I decided not to say Choice Specs because you would want to first set up Sunny Day to boost your fire type moves and straight away charge up Solar Beam, your attacks would be even stronger with Life Orb, example, the combination of Flamethrower+STAB+Blaze+Sun Boost+Life Orb's result is:
252 SpA Life Orb Typhlosion Solar Beam vs. 248 HP / 36 SpD Vaporeon: 302-356 (65.2 - 76.8%) -- guaranteed 2HKO after Leftovers recovery
How much the oppoment does:
0 SpA Vaporeon Surf vs. 0 HP / 36 SpD Typhlosion in Sun: 122-146 (41 - 49.1%) -- guaranteed 3HKO
Surf isn't the strongest move but it is literally only a three hit KO, also, Vaporeon has very high HP, which makes it difficult to beat.
If you are planning to make a Drought team and this is your Sunny Day Setter, then I would recommend giving it a Heat Rock instead of a Life Orb, also, the move I recommend changing Swift to would be Extrasensory or Focus Blast. Flamethrower is weaker than Fire Blast but it has lower accuracy but worth the sacrifice. If you are scared that you might miss the move, you can still use Flamethrower.
Here is the recommended set:
Typhlosion @ Heat Rock
EVs: 252 SpA / 4 SpD / 252 Spe
- Fire Blast/Flamethrower
- Solar Beam
- Sunny Day
- Extrasensory/Focus Blast
Choice Specs would be better for now as you can get it earlier in-game.
I've hoped I've helped!