I thought your failed obsidian tower experiment taught you that only the source block turns to obsidian - anything flowing will turn to cobblestone. The best way I know of to actually generate obsidian is with a pair of portals (destroy one, go through one, light one, then repeat), assuming they don't wind up just connecting to a single Nether portal. I'd sooner just create a small form in the Nether somewhere and do a bucket brigade to keep it safe.
Oh, I guess I never explained exactly how that tower happened did I. It
wasn't an attempt to make an Obsidian tower. I was trying to install lava lights inside the cliff-tower-thing (I really should name that...), in lieu of using torches. I put some lava behind glass and saw that it looked... kind of ugly. So when it came time to remove the lava, I broke the glass and it poured out. When I (thought) I had removed the source blocks, to my surprise it was still flowing, and I had no idea how to get rid of it other than pouring water on it. When I did, it turned into cobble. I then wondered if I could make a quick cobble tower with that method. As I added more and more lava blocks to the initial cobble column, and more and more cobble trying to make the tower wider, I wound up with the big mess that you saw when my turn was done.
So, yeah, long story short, it wasn't an attempt to make an Obsidian tower. That said, what I was just talking about in my previous post is making molds for the source blocks to go into. Imagine a rectangle of cobble, surrounded by a 1 block high wall and filled with dirt. The player removes one dirt block where they want to pour the lava, another for another bucket, another for another bucket, and so on until the entire mold is full of lava blocks. Then they pour water on it and create Obsidian. Mine it, fill it back up with dirt and repeat. That seems to be the most commonly used method of farming Obsidian, as far as I'm aware. There are tutorial videos on Youtube showing it too if you want to see it for yourself.