I'm kind of guessing that by "reliability", you're refering to each rounds' ability to get the job done, because as far as sure function goes, they'd be equal because it's based on your gun and ammo choice, not your cartridge.

Comparing these two cartridges is pretty much a waste of time-most hunters that only own one rifle that "does it all" would NEVER notice a difference in the two. Pretty much, other than the capabilities that the .308win has with heavy bullet, the two are identical in field performance...take my "hunting party" for example, I run a .30-06, my fiance runs a .308win, her brother runs a .270win, and a buddy of mine runs a 6.5x55swede (mauser), mine's a nudge for most powerful, the .308's almost a tie with me, and the other two pretty well tie for 3rd/4th, we knocked four deer out of a herd last season on one morning, we were all set up under the same pine on top of a ridge, the herd came out at 240yrds off, we whispered and agreed to wait until they came down to the river, which was about 200yrds off at the closest point that a trail met it, we picked whose deer was whose, and they came down, we knocked four deer into the mud, all with one shot, the exit wounds and trauma on each was almost the same, and all of them dropped within 15yrds of where they were hit.

For good hunters, either is capable of everything on the NA continent, although neither would be a first choice for the great bears, for most hunters (one rifle hunters for example, or those that only hunt deer species, maybe elk), they'll never notice the difference in the two.

Despite the fact that these two are pretty well evenly matched for deer, there are advantages to each vs. the other:

.270=flatter shooting for long range shooting (out to 600yrds-where the light bullets have lost a LOT of power)

.308win=more inherently accurate, slightly more powerful, and much more capable of heavier work because of its abilities with heavy bullets, .308win is a short action +you can also get a compact rifle in .308.

The only REALISTIC advantages are the .270's flat trajectory and the .308win's ability with heavy bullets...the .270win gives you a bit more leniancy with range estimation because it doesn't drop as quickly as the heavier, slower .308win, so when you shoot at a antelope at 300yrds that you thought was only at 250yrds, you might not miss. If you're planning on hunting elk, moose, caribou, sheep, goat, etc (heavier species), the .308win has an advantage because you can pack in heavier bullets, hunting moose with a .270win bullet at 130grns isn't comforting to most hunters, while the 180-200grn bullets of the .308win are a much better choice. The increased power of the .308win ties into this=when you're hunting deer, both are more than powerful enough so the .308's advantage is moot, while when you're going after something 300#+ (or tough species of sheep and goat), the .308win starts to pull ahead.

You can pick and choose from the above, or you can just pick which one you like better, you or your game will likely never notice the difference...hit a deer in the heart at 400yrds with the .270win and he's not going to look at his entry and exit wound and think, "that was only a .270, I don't think I'll die, but good thing it wasn't a .308!", he's just going to die.