I got a medium size bag, and its pros outweigh its cons IMO.

its not as bulky as an esky, can be stuffed out of the way when not in use, handles spikey fish and crays well, takes medium sized Mackies no probs, cleans easily, and holds ice well.

the only con is it could never hold ice longer than a decent ice box or esky could, so for the extended trips away, the esky wins.

I chose to get a bag because of the following; cheaper for the size of something which I can fit a mackie in, takes up less room on the boat, easier to move around, doubles as a cushion when not full of fish, I can carry it by myself and it can fold up at the front of the boat away from everything when not in use.

It's harder to clean because it's not rigid and I think they're not as well insulated as normal esky's but it still holds ice all day which is all I need.

You cant sit on a bag but you can sit on the esky.

A lot of us have upholstered cushions on the top of the esky to use as an extra seat.

Ice lasts much longer in an esky/icebox

 i have looked at the bags myself as the tub doesnt have a lot of deck space but as mentioned the bags dont hold the ice long. with our last boat the esky was a bonus seat and worked well but we rarely filled it lol. eskies would hold your cold drinks in place better too.bags still take up room on the deck when you have fish etc in it . i would go with esky over bag 

I stock the esky with block ice and can fit a couple of 70cm dhu's or pinks in there, anything bigger out comes the bag with a couple of blocks of ice. Never had a problem with spines, large madfish bag. If space is an issue a bag is the go.

Bag for me with a 5m boat. I make my own block ice so never had a problem with it all melting during a day's fishing. I've got a small esky that slips under the rear bench seats out of the way if I'm chasing B&B with the kids or crabbing

 Not really on the threads topic but if you do go for a bag make sure you use salt ice and you won't have any issue at all with it not staying frozen over the course of the day

 esky for me.  Have multiple eskies and a bag..  Bag struggles to hold ice for more than 8 hours up here in the pilbara.  even a cheap repco esky holds ice for 2 days.  Yeti holds ice for 4 days...  All using standard service station ice 

 I had a bag,ended up Selling it they don’t hold ice for very long. And once it’s loaded with fish and ice zipping and un-zipping becomes annoying because the bag just bulges 

cant go wrong with an icebox 

 Icebox all the way. Bags go saggy with too much fish/ ice and ice cant hold for too long. 

thanks guys! might stick with the ice box for now :)

I love mine...low weight and cheaper than 1100 eski...have a spot for it up front...block ice as above. Don't use it every trip but it's great as I hate fish curled up in the eski. I'll sit when in transit but other than that fishing boats don't need seats.

I'd always go with an esky, as others have said, they will keep things cold for longer, they make decent seats, and I'd be worried about the durability of a bag. 

 I use a madfish bag and salt ice, had the bag with salt ice in it for 2 days on the deck of the boat in the peak of summer and Salt Ice was still frozen at the end of the trip,

as Hutch said above if you want ice to last you need Salt Ice.