A better fan can help if it can push more air, measure in CFM. I'm not knowledgeable enough on all types of fans to know which one is better and by how much.
The main thing with PC cooling is to have air intake and roughly the same amount of fans exhaust.
I'll explain why but I'll keep it simple since that's the only understanding I have of the matter.
If I have one fan pushing air into a case (lets call it 1 unit of air per minute) then it is either going to increase the pressure in the case by 1 or 1 unit is going to be pushed out an exhaust port. That means that 1 fan not only has to use its energy to draw 1 unit of air in it also has to push one unit of air out. It's performing 2 job so it can only do each at half efficiency. It will also lose some efficiency because it is having to do 2 functions, also some other reasons like not being directly placed over the exhaust port, back pressure etc. So it might only be achieving 70% total efficiency due to losses (Random number plucked out of thin air)
If I now add one equal fan pushing air out of the case it frees the intake fan up to just draw air into the case. Both fans are moving 1 unit of air each, 1 in and 1 out. Both are more efficient due to less work load and less total loss.
Because of the way these efficiencies work you always want to try and have an equal push pull situation, There is no point in having 10 fans shoving air into a closed case and 1 exhausting. The internal pressure would build up and back pressure on all the fans would cause inefficiencies.
Based on this concept the best thing you can do is to have as many fans as your case allows with a equal amount on intake and exhaust duty.
Changing a fan on the side with one that can push more CFM could help because it is directing more of the air directly over the troubled components but it would still be best to ensure you have a properly configured fan setup before replacing already existing fans for small gains.
edit: I should add that due to a PC case not being 100% air tight this doesn't need to be 100% equal. There will be lots of places for excess pressure to exhaust or be drawn in if there is a slight negative pressure effect. It's all adds to the inefficiencies though.