Just like several other have been stating.
It all depends on how you intend to use your ship. Your play style etc.
For combat related stuff.
I switch between bi-weave and prismatics depending of if I go solo or play in wing, as in wing, we use healing beams, to recharge our shields.
Are you just going to hit and run missions, then prismatic most of the time offers an edge, like take out a few assassinate pirate lords missions, but if you are out to do long sessions of rez-hunting, etc where you expect to spend long time, then bi-weave are better, as this will quickly recharge between encounters.
For traders, I often go for the biggest shield I fit the smallest allowed slot. so for my Type 9, that is class 5 prismatic shield. I am also one of the lucky ones that have a legacy engineered engineered class 5 Prismatic for my trade Cutter. So I get over that magical 750T of cargo, while still having having a descent shield
My over engineered Type 9 have 1250 MJ raw shield and my Cutter have 2550 MJ raw shield. Which is enough to survive just about any encounter by NPC pirates.
Traders are not expected to stay long in fights, they just need to survive long enough to high wake, or until the security forces arrive. So here max MJ is beneficial. As your goal is to reach the destination and there recharge the shields, or if you have to high wake, visit another station to recharge the shields.
For exploration, I like the prismatics too,seems to work better on the bigger ships though, for example, I like to have over 1000 MJ on So I have my Ananconda with a class 3 Prismatic, that give me 1360 MJ of shields, great insurance for when I land on high G planets. I will survive a FREE FALL from 5+KM on Achenar 3, a 6.7G planet, with 4 pips to SYS. So for a reckles pilot like myslef, this is a great trade-off. And I do not feel that I have sacrifice to much jump range, as my Annie still do 71+ LY, perhaps not the most impressive range, but considering that I am packing seeker missiles, rail guns, mining laser, SLF fighter, etc, I think I am ready for most of the dangers a long exploration journey can surprise me with.
Being an owner of several prismatics, I say that class 5 are the ones that you probably want the most of! If you intend to have big fleet of various sized ships. I have just recently discovered that the 7 I already have is not enough... all the smaller ones, get 4 or each size, they are really cheap, so that is no cost, it is when you get to the class 6 and up they start to get really expensive with the class 8 being ridiculously expensive, so unless you have spare cash just lying around, only buy this size if you have a ship you expect to use it on. Like the Cutter or Type 10. The second considerations of you many of these is how much storage space you have to store these shields.
Also, worth noting, that when buying these, more costly modules, (just about all big modules, and class 8 in particular), visiting a Li Yong.-Rui controlled system will save you a big chunk of credits.
For example, the Class 8 prismatic 244 Million goes down to 202 Million with the Li Yon-Rui rebate.
So play around in tools like coriolis and compare your ships with or without prismatics, and do not forget about the bi-weaves, they do have their place too. It is harder to gauge their benefits. And do not be afraid of testing out "whacky" stuff, you might be surprised about what can work and etc. And depending on how you play, testing out whacky builds can be alot of fun.