Oh most definitely the non-bagged is fresher. The date of farmers market veg is how it physically looks to you when you handle, not by a date stamp. Also, the pre-cut stuff more than likely traveled hundres of miles before finding their new home on a store-shelf. Less chance that those items were allowed to ripen and grow naturally
In general, veg starts losing nutrients as soon as they're harvested. I'm not sure about greens but the rule of "bigger isn't always better", like with tomatoes and peppers may apply. Like, plants have a finite amount of nutrients they can pass on to their fruit, so if the produce is smaller, then its level of nutrients will be more concentrated.
I prefer my veg whole and take great satisfaction how of the entire preparation process, but in a pinch? Sure - grab a bag or 9.