I've tried a lot of different containers in which to grow plants. I didn't like plastic ones originally, because it always seemed like they got used once and thrown away. When I found out about making seed pots out of newspaper - by rolling it around a can and flattening the bottom - I was sold. It was free and eco-friendly at the same time. It didn't turn out to be so great. Once wet, they were very flimsy and hard to handle. I think the idea is to use something like a tray with low sides and cram these pots in and don't remove any until the seedlings are almost root bound. That seems like the only way these pots would be very good. The other drawback was making the number of pots that you might need - it could be a massive undertaking.
Something sturdier seemed to be using cardboard tubes from paper towels, toilet paper and wrapping paper. Once again it's a numbers issue - most people will not use enough of these products to have enough tubes for their seedlings.
This year I pulled out the seed trays I had collected last year or the year before. It looked like I had a lot, but once I started planting, I ran out fairly quickly - so I've had to prioritize a little and do some succession planting in my seed flats. I did splurge and buy biodegradable seed trays from Lowes - 4 8-pot trays for less than two dollars. At that price it didn't feel like a splurge at all.
After using those trays, I'm not very happy with them. Like the paper and cardboard, they get a little flimsy after a while, and the other thing I'm having problems with is that they dry out so quickly during the day. Almost none of the seeds I've tried to start in them are sprouting. My Better Boy hybrid tomatoes are growing, despite being dried out every day. It's all I can do to keep them alive.
So, I can say with certainty that I'll be using recycled plastic seed trays until I try peat pellets and soil blocks. When I try those - next spring maybe - I'll let you know how they work.