In my mind it's somewhat similar to comparing a Corvette to a Miata for those in the US, or perhaps a BMW M to Mini Cooper S
The Finn sails upwind Thur chop and waves, slicing thru them with half the pitching that a laser does. On a reach or run, when you are handling the sail one to one, you feel the power that the bigger sail and stiffer mast generates every time a puff hits. Downwind in breeze, when you are working the Finn hard, it's more squirrelly then a laser, IE the wipe out happens faster and harder, but the rides are more exhilarating.
Light air sailing, the finn's deeper cockpit is much more comfortable to deal with. No contorting yourself up around the dagger board ala a laser.
The hiking style is different, while you can straight leg a fiinn for short periods, you are normally hiked out in a bent leg style. It puts a lot of load on the knee joint, but the good news is that after 5-10 mins, your legs go numb so you don't really notice a burn in your legs the way you do in a laser. (It's better now, I raced them when you could still wear 20 kilos of water weight/clothing, which was an improvement to the times prior to that when you could pile on as much weight as you could handle in sweatshirts and weight jackets)
All in all, if you have the size for it, IMHO, the finn is a more challanging / rewarding and more interesting boat to sail. However the drawbacks of cost and lack of competition in most locations make the laser a better boat to compete in.
And, I guess, we all know that a competitive Finn is WAY more expensive and is typically sailed by a heavier sailor. In Europe though, the class is much more popular than in the States. As I recall, more than 100 boats entered a recent European Finn masters event.
Finns are one design boats defined only by the Finn Class rules.
Lasers are whatever thecopyright holders choose to build.
The quality of a Finn is determined by a number of factors including the skills of the builder and the demands of the purchaser.
The quality of the Laser is determined by the copyright holder and includes factors such as projected expenses from warranty claims, projected impact on reputation and by extension on the value of the stockholders paper.
If you would like to build your own Finn, all you need to do is build the boat according to the rules.
If you would like to build a laser, you need to go get a job at a factory where Lasers are made.
If you want an ultimate Finn, you can spend and spend and spend and never really get to ultimate.
If you want an ultimate laser, you must understand "ultimate" is any laser as all Lasers ever built have been exactly alike in every way.
If you want an excellent and durable class legal Finn sail, you call almost any sailmaker and order one.
If you want an excellent and durable class legal laser sail,......