I used a cooler for 20 some AG batches with good results. I switched to a heated keggle MLT with a false bottom a few weeks ago, and I really like it. When I am not heating my MLT, I keep it wrapped in closed cell foam sleeping mat (Walmart camping section, $6) and a 1" foam cover. I have seen no heat loss until I start recirculating. It is a simple process:
1) Heat up the water in the MLT (no preheating necessary)
2) Dough in and wrap the MLT
3) Start the recirc pump @ 30 minutes, run through a simple 2 wing sparge arm
4) Put the heat on low @ 50 minutes
5) Sparge when the tun hits 168 (75 minutes), sparge with the method of your choice.
One thing that I have noticed is that the wort is very clear with the 45 minutes of recirculation. There is also the "bling factor". I love the way my 2 tiered setup looks with 3 kegs. With the false bottom and pump suction, my batch sparging is much faster than using just gravity and a manifold in a cooler. All in all, I am glad I added a pump and heated MLT to my setup. I am more confident with my temperatures, as I can always adjust, and I am not lifting gallons and gallons of 180 degree water.