A quick disclaimer - I am a very new vaper myself, so I would recommend waiting for more experienced members to help, but here is a little info
The different coils will give you a different vaping experience because the resistance of the coil (measured in Ohms) will influence the wattage (power) going through the coil - a higher resistance (higher Ohms) will reduce the power, while a lower resistance (lower Ohms) will increase the power. The power (Watts) is also influenced by the Voltage of the battery, I believe you have fixed Voltage batteries as opposed to what are called Variable Voltage (VV) batteries (which allow you to adjust the voltage).
A little maths:
Watts = Volts x Volts / Ohms
I may be wrong, but I think your batteries are 3.7 Volt batteries (and are fixed at this Voltage, hence they are not VV's).
In my Protank 2 manual I have the following:
Suitable Voltage to different Resistance
Resistance Voltage
1.7 - 1.9 Ohms 3.1 - 3.3V
2.1 - 2.3 Ohms 3.4 - 3.7V
2.4 - 2.6 Ohms 3.8 - 4.1V
2.6 - 3.0 Ohms 4.2 - 4.5V
So for a 3.7V battery, the recommended resistance coils to use are around 2.3 Ohms. But naturally people want to try lower resistance coils to try to increase the Power (Watts) and heat that coil up even more. With a given (fixed) Voltage, resistance has an inverse-linear relationship with Power, meaning whatever you change the resistance by then the opposite will happen to the Power: if you decrease the resistance then Power will increase by the same factor.
Remember, higher Power (Watts) heats up the coil more, but will drain your battery faster. A 1.8 Ohm coil has approximately 20% less resistance than a 2.2 Ohm coil, so you will get 20% more power (Watts) going through your coil to heat the ejuice, but will have 20% less battery life.
Choosing coil resistances is completely subjective. It's a matter of trying different things out and finding what you like. Also I believe the composition of the ejuice will influence your preference for coil resistance. I've got a relatively thick ejuice in my Protank 2 (relatively high in VG which is thicker than PG). It seems the Protank 2's are not the best for thicker juices as the design isn't the most effective for getting thick ejuice onto the wick at the coil - therefore the wick may not always be saturated enough to get a good vape and thus 'dry hits' can result. Therefore I have lowered the Voltage on my battery (as it is a Variable Voltage battery) to reduce the Power going through the coil which is easier on the wick and seems to allow it to saturate with ejuice better when vaping alot (this is my experience after a few days anyway).
The coil heads are relatively cheap though, so it may be worth picking up a 1.8 Ohm coil to try in your Protank 2. If your batteries are rated at lower than 3.7V then the Protank 2 manual recommends these coils anyway.
I keep getting distracted while I've been writing this post, I hope I've not made any glaring errors, remember I'm a noob too! Hopefully someone else will maybe enlighten both of us with some more info
