I've used GoLocker and Widget Locker. Widget Locker is 10x better, more smooth and it almost literally replaces the new lockscreen. it has about 10 built in lock themes that are pretty standard, including Ice Cream Sandwhich, Froyo, Gingerbread, Honeycomb.
I definitely recommend it's purchase if you're looking for a new lockscreen. It's also super-customizable.
Sometimes you do still have that delay when it switches to the lockscreen, but it's not nearly as bad as Go Locker. usually the lagged lockscreen happens if you turn the screen off then turn it on right away. If you turn the screen off and wait a couple seconds, it grabs the Widget Locker screen completely when you turn it back on.