frequent
We bat this around on a regular basis concerning the .243. You might search some other threads in these forums.
Essentially there are two schools of thought, heavy bullet v. light bullet. There's a sub theory that includes the premium/bullet v. common cup/core bullet.
I'm a heavy bullet guy myself for .243 on deer and endorse the 100 gr Nosler Partion, which is usually considered a sort of premium slug. I believe Hornady offers the Partion in .243 as factory ammo, and surely others do as well.
I'm not sure you need a premium/bonded/partition slug from the .243 in 100 gr weight, but such bullet offers a bit of an edge on penetration with shots at odd angles and encountering larger bones.
You will hear from guys who use lighter, faster expanding slugs in .243 as well, very effectively. Say 70-90 grains. I don't doubt it a bit. Under good circumstances, picking your shots, unhurried and likely shooting from support, and a clear, unstartled anmimal, one of the lighter quick openers will be grim death on the rib cage of the typical whitetail. I
Whatever you pick, light or heavy, do not make the mistake of selecting a bullet made for varmint work, say 55- 70 grains. These are intended to "blow up" on groundhog and coyote sized critters and are not big game bullets.