Really depends on your style of fishing.  If you just sit in one spot and don't move much and don't have a shack to warm up in then I would want the warmest boot you can get, I would not worry about weight.  I tend to hole hop and a lot of the lakes I fish I have to walk on so my Lacrosse Aeroheads I bought for hunting are warm enough.  If I can drive on the lake I have my hub style shack with a heater so again the hunting boot is good enough.  It doesn't take that much moving around to keep warm even on cold days.  My holes are usually within 30 yards of where I set up and that little walking from hole to hole does wonders.  I get colder sitting in a deer stand when it is 30 degrees than I do ice fishing. And the Aeroheads are 18" tall so you stay dry and don't get snow over the top of them.  I would try what ever boot you currently own and decide for yourself if you need a warmer/heavier boot.  But I prefer a lighter boot because of my style.

"Best" boots and warm clothing is really subjective and based on the physical traits and conditions of those wearing them.

I'm 52 and have good circulation, a dude who's 38 may be worse off than I. So the same boots for each of us simply won't be the same.

Socks that wick moisture are key.  I have been fishing in my LaCrosse Ice Kings for well over a decade and they keep my feet dry and warm.  But they are far from light weight.  Maybe newer versions are lighter.  The boot I'm interested in is the boot that Ice Armor/Clam has recently come out with.  Looks like they're made specifically for ice fishing.  They're rubber and have a removable wool liner.  Rated to -40 degrees.  If it's any colder than that, I'll be in my chair watching something on Netflix.  I have not seen any reviews on them yet so I'll probably just wear the old Ice Kings until next season when more info/opinions are out there.

Just my 2c

it all depends on the person to and socks. Start with good wool socks and go from there. My feet sweat so i wear lightweight smartwool socks to wick the moisture. Then i wear 800 gram thinsulate irish setter mountain claws. They are under 5 pounds for the pair, fit my feet great and have a wide toe so i can wiggle my toes to keep circulation in them. So for me that is the perfect boot. I had some rocky blizzard stalkers that im convinced one boot was missing thinsulate in the toe because two of my toes would always get really cold. It all depends on the person really. Also carry extra socks incase your feet get wet or really sweaty. Then you can wear dry ones and dry the wet ones on the heater. 

In 32 years on the ice, I've tried several different boots. I found the white bunny boots to be the warmest, and have worn out two pair had thinsulate booties over cotton socks, and felt innersoles.As warm as they are, at times my feet got chilly, Last year I wanted to try newer, lighter technology. After much research, and reading of reviews. I went with Baffin Impact boots. With just one pair of cotton socks, they are the warmest, lightest, most comfortable boots I've ever wore. One of these boots weighs about the same as my pair of bunnies.

Hands down, Baffin Impact boot. I purchased a pair this year and never even had to think of wool socks. I've been wearing just my regular socks all year. Light weight and rated for 145 below zero! Tested in Antarctica. They may be pricey but I'll never have to purchase wool socks again. My feet don't even sweat in them.

I'm with Robbollio on the Mickey, throw a dozen 1/4" screws in the bottom and they can't be beat

One thing I've found as my feet use to get cold. Pair of nylon sweat wick socks followed by good pair of wool. The most important thing is by one size bigger than you need to give your foot room to breath. That has made a huge difference for me. I use lacrosse pack boots for ice fishing. Little bulky but with either 4wheeler or truck don't have to walk too far with them.

For years I had the Cabelas Infernos a good boot but I wanted something different so I went with a pair of Muck Arctic Pros. The Mucks are very comfortable but I did get cold feet when the temps drop below 15. This year I got a pair of Sorel Glacier XT and this boot is great, they are water proof light,very warm

http://www.cabelas.com/product/footwear/men-s-footwear/men-s-pac-winter-boots|/pc/104797980/c/104747580/sc/103959180/sorel-174-glacier-8482-xt-pac-boots/1827097.uts?destination=%2Fcatalog%2Fbrowse%2Fmens-pac-winter-boots%2F_%2FN-1107989%2FNs-CATEGORY_SEQ_103959180

LaCrosse Ice KIngs and Lacrosse Alpha Burly Pro 1600 are the two boots I own. I wear them both a lot, and both serve me well. The Burly's are lighter by quite a lot. Socks are super important. Eliminate cotton from your wardrobe and you'll find yourself much warmer out there!!