I use baby food jars just because they are inexpensive and fairly easy to obtain. I don't use the jar lids though. I get special caps for flasking from here.
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Also, they have some really nice glassware that they sell there too. Works just as well. I have used both babyfood jars and lab jars like they sell on that website.
For me it really depends on the amount of room I need or how much space the plants need.
If you don't sow the seeds to heavy, you can get away with using smaller jars.