I'm surprised to see the lack of discussion of the Sunny Day set. I run:
Timid
-Flamethrower (I feel like missing FB is more likely to be a problem with this thing than failing to KO with FT)
-Dark Pulse
-Solarbeam
-Sunny Day
This is how things usually work: Switch in on something it scares off. Use Sunny Day as they switch into a Rotom-W or another bulky water like Vaporeon. KO with Solarbeam. If they switch Solarbeam + FT or Dark Pulse will more than likely 2HKO whatever comes in. The ability to shut down its most common ostensible counters (bulky waters) makes this better than the Nasty Plot set. It's also true that if TTar switches in on the turn you set up the sun, your sun overtakes Ttar's sand and it either has to switch out or get destroyed by a Solarbeam.
Timid
-Flamethrower (I feel like missing FB is more likely to be a problem with this thing than failing to KO with FT)
-Dark Pulse
-Solarbeam
-Sunny Day
This is how things usually work: Switch in on something it scares off. Use Sunny Day as they switch into a Rotom-W or another bulky water like Vaporeon. KO with Solarbeam. If they switch Solarbeam + FT or Dark Pulse will more than likely 2HKO whatever comes in. The ability to shut down its most common ostensible counters (bulky waters) makes this better than the Nasty Plot set. It's also true that if TTar switches in on the turn you set up the sun, your sun overtakes Ttar's sand and it either has to switch out or get destroyed by a Solarbeam.