I think your odds are best with the one-time-onlies for a big win, but the instants are rewarding for small wins. Right now, the Cheerios sweeps is paying off for a lot of us. If you win the max of 10 times, that's $50. (You can do a search on "Cheerios" to find it.)
You'd be surprised, though, that you can win a daily with just one entry. One year the HGTV Dream Home was won with just one entry, for example. So I try to enter everything that appeals to me at least once. Others might have hundreds of entries in a particular sweeps and I might have, say, 14, but I still feel I can win.
So, I agree with Marli, enter the ones that make you happiest to dream of winning. I, too, am impressed that you have any time for it at all. Good luck!
Best 10/2009 win: 47inch LCD 1080p HDTV including a TV stand, Nintendo Wii and two games (1 of 10 Grand Prizes)
Best 11/2009 win: Kindle (1 of 7 Grand Prizes)
Best 12/2009 win: $5 Home Depot gift card (1 of 10,500 fourth prizes)
Best 1/2010 wins: Loacker bag with 8 mugs (1 of 1000)--from my very first sweeping entry in the New Year!
................................. Philips Prestigo Universal Remote Control (1 of 5 remotes out of 50 second place prizes)
................................. $5 check from Cheerios (now a total of 4 out of 40,608) actual money--woo!
Best 2/2010 win: stainless steel tongs, $2.66