Where to place the flow sensor depends a bit on which flow sensor you have.

If one of the High Flow, flow sensors, it can go anywhere in the loop. The flow rate is the same throughout the loop.

If one of the MPS flow sensors, it is recommended you have at least 5 cm of straight tubing before and after the sensor to reduce the impact of turbulence introduced by angular fittings.

The flow will be the same throughout the loop, unless you have something in parallel.
It cannot be faster in one area of the loop, and not the rest of the loop.
One consideration is that there be some straight sections of the tubing before and after the Sensor.

RodeoGeorge

Quoted from "Bartdude"

Reason I asked, I figured that at the end of a loop after the restrictions from blocks and rads the flow would be reduced but directly after the pump it would be at its strongest or am I missing something? ATM I have a Bitspower flow sensor (I know) I will be changing it for an Aquacomputer. Can you recommend which is best, the MPS or the high flow?

At the end of a loop, the fluid pressure will be decreased due to restriction along the loop, with a resultant flow rate decrease in the loop, but the flow rate will be the same throughout the loop.

Just after the pump, the pressure is the highest.
Just before the reservoir (last item in loop) the pressure is the lowest
If the pressure is zero by the end of the loop, your flow rate will be zero, and it will be zero for the entire loop.

As to which aquacomputer flow sensor is better?

MPS flow sensor

• is petite
  
• quiet (no ticking sound from an impeller rotating)
  
• for best performance requires minimum 5 cm on either side of the sensor before angular fittings can be added
  
• requires calibration for best accuracy if desired
  
• the rubber gasket at the sensor probes appears to waste away over time, requiring replacement.
  I do not know what that time period is but maybe around a year or so
  

I am currently waiting for replacement gaskets from aquacomputer to replace in my 1.5 year old units.

Highflow flow sensor

• 2 to 3 times the size of an MPS sensor
  
• has a ticking sounds at higher flow rates
  
• angular fittings can be added directly to the flow sensor
  
• does not require calibration
  
• I do not know about the sealing around the impeller shaft
  

I performed an air pressure drop test on a brand new Highflow USB/aquabus flow sensor and it showed a pressure drop from 0.5 bar to 0.42 bar over approximately 15 minutes.
I do not know what is up with that, but I will contact tech support after I receive the new gaskets for the MPS sensors to see how that works.

At his time I cannot recommend one over the other. I need to see how the MPS replacement gaskets work out, and what aquacomputer says about the Highflow unit pressure drop.

I love my high flow sensor. Don't have to worry about things like you would with the MPS sensor and it's one less MPS for the Aquaero.

I too went from the MPS400 to the High Flow Sensor on my last build.
I have used six MPS400 Sensors in past builds, and all of them over time have stopped working.
The High Pressure Sensors on the other hand have been bullet proof, and can be installed without the need for "straight runs" into and out of the Sensor.

I ordered an extra Hi Flow Sensor for my last build which I did not use, and just put it up on eBay for a great price.

RodeoGeorge