How do you decide type, rate, and direction of flow in your tanks?

[TravisN]

I've only had my aquarium (planted 40G breeder community tank) for a couple of years now and still consider myself an amateur, but thought this was an interesting topic for discussion. How do you decide on the type, direction, and rate of flow for your aquariums? I have a canister filter and it occurred to me that I have the option of using a distributor nozzle, a spray bar, using steel pipes, etc. On top of that, I could decide to direct the flow from left to right, front to back, or diagonally across. I could have a vertical spray bar in a corner creating a cycle effect.  

What things do you take into consideration when deciding the flow in your aquarium or what are the pros/cons of the different methods?

Edit: Thanks for the replies so far! Just wanted to clarify that I'm not looking for help or advice. There's obviously no one way to do this. I thought it would be interesting to hear different perspectives. 

Edited July 31 by TravisN

[nabokovfan87]

The old "rule of thumb" was to go from one corner, diagonal to the opposing corner.

 

[Pepere]

This might help.

[Pepere]

Personally I dont follow green aqua advice.  I have the outlet of my canister filter feed a spray bar on the back of my tank, underwater blowing to the front of the tank creating a back to front, down glass, back across the gravel circular flow.  The flow agitates the surface of the water a bit for gas exchange.

I  bought fluval 207s for a 29 gallon tank which has plenty of filtration, but at 121 gallons per hour filter flow it isnt meeting the 10 times reccomendation of flow.  
 

I found it did a decent job keeping co2 churning on 40%of the tank side the diffuser is, in a circular flow pattern, but not the other 60% of the tank.  
 

To that end I added 2 small 3 watt wavemakers, 1 just over the diffuser pushing to the front and downward, and another on opposite side if the tank returning flow across the top of the tank just below the laminar flow of the spray bar.  
 

These are on a timer to coincide with the time the co2 solenoid is on.  I very clearly meet the 10 times flow per hour now when the wavemakers are on.  The fish have areas of low flow to have a break, and they appear to enjoy swimming against the current.  The whole tank has suspended co2 bubbles..

I think if I were to do it over I would opt for larger canister filters to have more flow.  It would reduce current carrying wires in the tank and visual clutter.  I think I would stay with the spray bar.  The glass lily pipe option Green Aqua prefers require a lidless tank.

[Gwallace]

I don't want a ton of direct flow in my tanks as they all have floating plants.  I use spraybars on the canister outputs swiveled around so they point back at the end glass.  This disperses the flow slightly downward and gives me a gentle current from one of the tank to the other without disrupting the floaters.