Pennzoil conventional is highly regarded here, and the new Havoline looks like a good oil too.
Pennzoil, Quaker State, Valvoline, Castrol and Havoline all have their own little advantages and disadvantages but are pretty close.
The Havoline starts out thinner than most of these oils, but after being run holds onto its viscosity better. More consistent oil.
The Pennzoil has really good base oils and a strong additive package, when in doubt grab the yellow bottle.
Castrol's oil seems to be geared towards being a high temperature oil, and for certain additives like calcium is packing as much punch as the Pennzoil.
The Valvoline and Quaker State seem to be pretty middle of the line. I've never liked the green bottle, personal preference, but I do like Valvoline. It just seems like such a straight, simple, safe choice in oil and from what I have read, out of 5W-30 conventionals is the best from cold starts. It looks delicious, as well.
Really, it's a matter of preference.