Mnemonica

I used osterlinds BCS,
but will convert to mnemonica

Aronson

Mnemonica

Osterlind

As for me, what first got me hooked on stacks was the basic Si Stebbins stack (CHaSeD order) that I found in a library book. I still use it at times when I perform a trick that works perfectly well with the Si Stebbins stack, but I've abandoned CHaSeD order in favor of SHoCkeD order, which makes a lot more sense to me.

When I discovered Richard Osterlind's BCS I immediately fell in love with it and used it whenever I could. I eventually switched over to Doug Dyment's DAO stack. However, later I memorized the BCS (making it MBCS for me), so now BCS has once again become my main non-Si-Stebbins-like stack.

As for memorized deck work, my first true memorized deck was Joyal SHoCkeD (after trying to learn the Nikola stack and subsequently giving up). Then I learned and dabbled a bit with Doug Dyment's QuickerStack (which I still use every once in a while). Some time later I was inspired by Martin Joyal's work to create my own stack, and soon after that I memorized Osterlind's BCS/MBCS stack (as I mentioned above) which is now my main memdeck.

To summarize:

For non-memdeck work, I use the BCS, with occasional use of the traditional Si Stebbins stack in SHoCkeD order.

For memdeck work, I use the MBCS (the Memorized Breakthrough Card System).

Overall, if I had to pick just one, I would say I use Osterlind's MBCS stack.

Mnemonica

Mnemonica. Studying Woody Aragon's now. Will probably use both.

I use a stack of my own which was inspired by Doug Dyment's "Quikstack." Karl Fulves published it in "Prolix #8." Many of the classic Si Stebbins quick ways to know how many cards are removed from the deck also work with this (as they would with Doug's stack). I find that combination together with knowing where any card is in the deck (and vice versa), makes a nice combination.

I've used almost all the simple cyclical stacks at one time or another for particular situations. Lately I often use a version of Docc Hilford's "Syndrome" deck using "8 Kings". This is very nice as the deck can be both riffle-shuffled (face-up) and overhand-shuffled (face-down), without ruining the way the deck works. Of course, this is not a true memorized deck.

Richar Osterlinds breakthrough card system.

I only use Si Stebbims (learning the Aronson stack now).

Mnemonica

Mnemonica
BCS (Ostelind)

Mnemonica
Kindergarten Stack (Michael Weber)

Aronson.

Joyal stack with some minor variations.

I use Mnemonica mainly.
Sometimes Si Stebbins 3 or 4
When King Jack Stack (I think I found this in a Jack Kent Tiller book) suits change red red black black on A 2 3 4 so it looks random
Use stay stack a lot in full deck and small packet effects
At the moment though, a stack which I am playing with and is just great is one I found in Woody Aragons Book in English. It's a stay stack Memorized ESP deck that can be fairly shuffled dealt and cut, but remains in perfect order. It's pretty astounding as are all the routines in that great book.
Who killed Lilly Long Legs by Simon Lovell
Perfect from Mr Bannons new book Zero
1-0-1 deck
Total Surrender stack from Art Decko
I am thinking of using Square Deal stack from same book too.
Half of Lennart Greens Recycling Poker Stack
Higgledy Piggledy Poker stack (my name, original is in Appocalypse, but my Memory not too good. Similar recycling poker stack but with three rounds of dealing getting progressively better. Think it might be called progressive poker or something like that. Great stack.
Big Deal by Joshua Jay
I like stacks

Aronson, since 1979.

Stebbins

Mnemonica.
I always try to left prepared the stack when I finish training. It is my last job of every day.