For non-designers, telling whether something is designed well or not usually is a feeling. It would be very helpful if it could be put into words why each logo was in each category. That usually turns a feeling into substance that can be reused.
StockTwits has a lot of small issues with its logotype which contributes to its 'average' label. The type is not kerned correctly, uses an awkward typeface (look at, for example, the w), and has that odd messages icon on top of the i.
SimpleGeo, on the other hand, has a beautifully kerned typeface, contains a more recognizable logo (note the compass; this is something that can eventually become instantly recognizable), and is overall simpler- by that, I mean that it can be used in a large variety of mediums (note the color in StockTwits' logo).
Overall, the main difference is in the type itself- tall, awkward, and lanky type versus medium, large, and overall more visually clear type.