I like a mix of easy and tough encounters. I like a mix of encounters with combat and non-combat, and to have all encounters combat is way too boring. I was in a game that was all combat, even all random encounters turned into slugfests because the DM though it was fun. I suggested to him that he might want to tone down the amount of combats he had, but he didn't listen, and two of us have left his group since.
On a side note, whoever thinks kobolds are easy all the time is gravely mistaken. In the other game I am currently still in, our party was tracking a group of kobolds through a forest, and the tracks led to a kobold encampment, with a few tents and we could see probably twenty kobolds milling about. Some on dire weasels, some unarmored, and a strange blue-colored kobold (who was a half-dragon, but at that time we didn't know that). These kobolds had attacked a couple wagons, and we wanted to try to save anyone we could find, and the ranger wanted to just kill them (favored enemy kicked in).
We lost one person, the barbarian cleric was taken down to 3 hp, the druid down to 1 hp, the ranger down to 5 hp, and mine was down to 12 hp (Monk2/Fighter1/half dragon). That was a blast, and when the fighter fell and the half dragon of theirs blew it's lightning at the fighter, we all ran. Not only that, but all the kobolds were at least 2nd level warriors/sorcerers. And we killed 16 kobolds and there were still over 20 left (some were in the tents when we attacked).