From a target shooters perspective:
The 243 and the 270 are totally different cartidges.
If you reload, The 243 shoots flatter than the 270. Bullets with much higger BC are available in that diameter.
The 243 is night and day the better pick for varmints. Even though its a little big for that too. Less recoil/ easier to shoot for presision work.
Afrer 1000 yards the 270's energy has bled out so much that the 243 has nearly
Matched it.
The 270 win is a hunting mans caliber. It is/was intended to shoot big game form its onset.
The 270 has more energy than the 243, therefore by default(physics) can kill lager animals easier.
The .277 cal is seriously handycapped by a lack of high BC bullets.
If there was higher BC bullets like the 168gr .284 BergerVLD, it would shine for long range target as well as hunting!
I like both, shot many animals With both.
I have shot both out to 1000 yards many times, and the 243 out to 1300.
The 243 with 108 grain bergers just dont get easier to shoot long range. Fun stuff!
Both cartridges are great hunting calibers, in thier own class.
This time next year I will be shooting a custom 270 win tactical rifle. My goal is 1760 yards. I want to post a group with it at that distance. It will take some work, but I know it can be done.
Just pick one that suits your mood and go for it. Its all fun!