For the first time since I was a teenager, I found myself weeding and whacking a yard this summer.
At my place, I used an old corded Black and Decker string trimmer and a new Black and Decker cordless string trimmer. Both of them work great, and putting new line into an old spool, or replacing a spool, are easy processes. I just spin new line onto an old spool, thread it through one hole, and I am done. The line feeds out automatically on both the old and the new trimmer, and I rarely have to take the spool out unless I try to cut something that is too thick and tough, like a big blackberry vine.
I also helped a friend in Portland weedwhack his yard this summer (hey, I am a nice guy) and used his corded Ryobi string trimmer. He warned me ahead of time that putting new line in the Ryobi was a pain in the neck. Sure enough, trying to put new line (as opposed to buying a pre-threaded spool) was incredibly difficult. I had to thread the line both ways and put both ends through a hole in the spool. I could not simply thread a bunch of line on the spool until it looked full -- no, I had to cut a length of about five feet of line in advance and guess whether it would be too long. It took me a full hour to figure out and thread the line. I would not recommend a Ryobi trimmer at all.
Here are directions on how to re-string a Ryobi weedeater, from:
You have to be sure to cut no more than 25 feet, or you will find yourself screwed. With the Black and Decker, putting new string on a spool is so much easier! Just wind on as much string as you want and until the spool looks full, then pop it in.