You don't want either of those. For the price range you're talking about you won't get a very good 1440p 27" monitor. For the 250.00-ish range, this is the best option:
PCPartPicker part list /
Price breakdown by merchant
Monitor: Asus VG248QE 144Hz 24.0" Monitor ($264.99 @ Amazon)
Total: $264.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-17 14:51 EDT-0400
If you can afford, or wait and save up for it, this would be a superior choice for the size and resolution you've outlined:
PCPartPicker part list /
Price breakdown by merchant
Monitor: BenQ GW2765HT 60Hz 27.0" Monitor ($449.99 @ Amazon)
Total: $449.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-17 14:58 EDT-0400