I'm not going to go into too much detail here about what spores are and how mycelium works, I'll just briefly touch on the pros and cons. The first downside to spores is the additional time required for spores to germinate (can be around 5 days) before they even start producing hyphae. The most problematic issue with spores is that they are not a sterile product. They are non sterile spores suspended in sterile distilled water. When collecting spore prints from the gills of mushrooms, there can be contaminants present which pop up during the growing process.
Conclusion: Using spores to grain is easier but is not going to produce consistent successful grows when using directly with grain.
Liquid culture is mycelium suspended in a sterile nutrient broth, it is a sterile product when produced correctly. There is no additional waiting time for LC as it's established mycelium already.
Conclusion: You won't get problems with contamination using liquid culture if everything goes well.