Tbh... I was having the same dilema when I was levelling up my toons. I was all for gearing them up to run content at both 60 and 70, but in the end decided just to keep levelling up to 80. From 60-70 you can pick or choose the quests you want, levelling is easy... 70-80 on the other hand is another proposition. I ran every quest, as this was the only way to ensure that you got the relevant quest chains. I managed to hit 80 with about 2 zones worth of quests left to complete (around 10,000g - spread over a team of 5). Now I'm concentrating on gearing them at 80, using professions to equip them to start on Heroic content. Bottom line... Stick with quest rewards until you get to 80.