Most often I use fluorocarbon level line. Size 3号. Sometimes 2.5号 or 3.5号.
Also often fish with Fujino Line Soft Tenkara Line - that is a tapered nylon line, 5meters or 4meters. Or a TUSA version that is 4.5m.
I sometimes do practice casting with Fujino Lone Long Soft Tenkara Line, mostly with 7m or 8m line. Once in a while I will fish with the 7m, but not often.
Mostly I fish with 4.5m or 5m line. Sometimes 4m, or 5.5m line. Mostly with 4m rod. Less often with 4.5m rod. Or 3.9m rod. If I fish with 3.6m rod or shorter rod, I use shorter lines. Mostly I fish with a line length = 1.125x or 1.25x rod length. Plus 0.8m to 1.5m of tippet. Either fluorocarbon or nylon tippet.
Among the lines I use, or have tried are these:
Fluorocarbon level lines
http://yoz-ami.jp/276 3.0 号
http://yoz-ami.jp/184 2.5 号
http://www.u-nissin.co.jp/item/672 2.5 号 or 3.0 号
http://www.u-nissin.co.jp/item/669 3.0 号
http://www.linesystem.jp/1046 3.0 号 or 3.5 号
https://www.sunline.co.jp/sl_html2/products/bass/fc_sniper_azayaka.html 2.5 号 or 3.0 号
http://www.tenkarausa.com/shop/product_info.php/products_id/158 3.5 号 & 4.5 号
Nylon tapered line
http://www.fujinoline.co.jp/archives/3085.html 4m or 5m
http://www.fujinoline.co.jp/archives/3419.html Mostly just for practice to try to improve my casting rhythm, maybe once each season I will fish with the 7m length. But mostly I don’t like fishing with a line that long.
Zxion straight line - 5m
Furled lines, but I do not use them often, probably have not used them over the last 3 seasons.
I also have a couple of fluorocarbon tapered lines I still fish with, they were tied from different sizes of fc line, that Tenkarabum made and sold years ago. I think I have 3 different lengths, if I recall correctly, the longest being 6m.