Here is the deal. I find weekly lineups to be MUCH better and here is why.
First of all the "injury" factor may be a bit frustrating but the reality is that it effects ALL teams in the league exactly the same so that balances out completely. Just as much as it pains you to see a guy go down on Tuesday and you can't replace him till Sunday, it helps you when this also happens to the other 9 or 11 teams in your league. This is a wash.
What I like better about the weekly lineup is that it prevents a true advantage for the guy who happens to not have a job, not go to school and literally sit in front of his computer all day long with no life. You'll find many of these sorts around here which makes perfect sense why they LOVE weekly lineups. They basically can listen to each and every game and the moment they hear some new guy is going to get a spot start on the Devil Ray's they can slide them into their rotation immediately.
So what happens is when you have 2-3 guys in the league who are extremely active and the rest of the guys are active to the point where they check intot he league once or twice a day, it gives those 2-3 guys a distinct advantage. Once the rest of the league finds this out it turns the rest of the teams into people who don't really care that much because they don't feel they can compete with the time the others put in.
I mean heck, what do you do when you take a 2-3 day vacation? It's bad enough in a weekly league where you may miss on a few transactions but even worse in a daily league where you may not start somebody who needs to be started.
I've played in both and I consider myself a pretty active fantasy player and I can tell you, from the health of the league in its entirety, weekly league's are better.
Only if you had a group of guys who were ALL true die-hards would I recomend a daily league.