Well, I don't know what you want to use them for (presumably a physical sweeper), nor in which tier you want to use them, but in any case:
Cacturne shouldn't be used outside of NU (despite Smogon's RU tier ranking for it). While it has the same typing as Shiftry, it has appalling speed and defences. At least Shiftry's speed in the sun will give it an advantage against Pokemon like Scizor.
Cacturne @ Life Orb
Ability: Water Absorb
EVs: 252 Atk, 252 Speed
If you want, Cacturne can serve as a Spiker as well, but I'd suggest using something else instead, like Garbodor, making your Cacturne a physical sweeper.
Breloom can fulfil many roles, either going as an all out attacker with its Technician ability, or a staller/ Focus Puncher with Poison Heal and Substitute.
Breloom @ Toxic Orb
Ability: Poison Heal
EVs: 252 Atk, 252 Speed, 4 HP
Breloom @ Life Orb
EVs: 252 Atk, 252 Speed, 4 Hp
Breloom for OU, Cacturne for NU. It's not as if these Pokemon can play outside of their tiers anyway (well you can use a Cacturne in OU, but it'd just be fodder for a Scizor). If this is just a random question as to which is the better physical sweeper: Breloom. While both Pokemon have a x4 weakness, Breloom is faster and has brilliant abilities for it to get past its x4 flying weakness.