That Kenmore 73055 rates wery well, number 3 in the 5000-6000 BTU category.
The Panansonic CW-XC63HU is rated number 2 in that category.
The number one rating goes to the 5000 BTU, 10.7 EER Whirlpool ACQ058MM, a CR Best Buy for $160.
Number 5 is the 5200 BTU, 10.8 EER LG LW5200ER for $180.
Forget #4; It's a Friedrich for $400.
For the larger unit, the Kenmore 76129 is 12,300 BTU, 10.8 BTU, and rated number 3 for $450.
#1 in the 9800-12,500 BTU category is rated a Best Buy. It's a Panasonic CW-XC103HU, 9800 BTU, 10.8 EER, for $330.
#2 is the LG LW1000ER, 10000 BTU, 11.0 EER, for $350.
Prices above are the ones listed in the magazine.
EDIT: If that large AC you're looking at from Sears is the 76129, $350 looks like a great price. For the smaller one, you can get much cheaper units on sale, some for as low as $100, but they won't be as quiet and efficient as you're looking for. You won't go wrong with that Sears 73055, IMHO.