4 and 5 inch are standard.

I normally use 4 inch for smalllies and 5 if I am specifically targeting largemouth.

I also like the 4 inch slims for dropshotting.

5" for all situations LM or SM it doesn't get any better.
Russ

I like to start with 5", but if it seems like there's not much going on, I change to 4". While I have caught keeper Smallies on the 5", I generally find the 4" produces more Smallies, and bigger Smallies. It seems like while they can eat the 5", only the smaller ones are aggressive enough to eat the bigger bait.

A key factor for me has been the realization that when just a little breeze comes up, the change to Whacky Rig produces more feesh. Less light penetration =  increased fish activity. It also happens to anchor the bait in the water so well, that the feel of the bite is much better. Just don't overwork the bait. It doesn't take much wind or much twitchin'.  Whacky Riggin' a Senko in dead calm won't produce many bites, even in relatively murky water.  I haven't tried Whacky rigging 5" Senkos yet, but I will. Got bigger Gamakatsu circle hooks for the job, and a rod that will be perfect....C&R, Steve
PS: What happened to "The Glow"?

Ah, yes. I can see why it would produce so well.    C&R, Steve

http://ia.ec.imdb.com/media/imdb/01/I/11/86/58m.jpg

What ever Smitty!   Lucky dawg!

Carlos

They're all good. You can't really go wrong with a senko by the way. No matter what size! Just keep telling yourself size doesn't matter. That's what I tell myself, OPPS!!!

LMAO guys, size does matter, just ask the wife.  And Stu, you can borrow my senko any time.

Mark