In the current meta.
Level up to 4 after third creep round
Level up to 5 round before first Carousel, unless you already have a couple of two star units.
Level up to 6 after second Carousel
Econ to wolves.
If you got what you need, Econ to next Carousel then level to 7, if you don't roll to get what you need and level to 7 at Raptors.
The only time you wouldn't do this is when you're high rolling (already have several two star units that you can 3 star) in which case you don't level at all until you have your units.
With the meta being as incredibly aggressive as it is, losing at Krugs shouldn't happen as you'll have 5 units, or enough two stars to do it.
In case anyone is wondering why leveling is so aggressive at the moment
You level for several reasons:
-
Availability of stronger units sooner, with Morgana, Kennen, Volibear and Aatrox being hotly contested, you want to get them coming up as soon as you can.
-
Getting the core of your composition as soon as possible, synergies help a lot, you'll have core units you're wanting and you'll want them as soon as possible.
-
Player damage mitigation, more units on the field means less chance of losing by large margins and less chance of taking a lot of early damage that can be hard to recover from.
I'm seeing players even in Plat trying to use the econ strategy only to get eliminated before wolves, right now you shouldn't be trying to econ early unless you're doing high roll and that's entirely dependent on getting several 2 star units before the end of the initial creep waves. Econ only comes in now when you have your composition core and are at a place where you can mitigate/win fights more often than not.