I decided to write this due to seeing so many "What ID should I pick?" and so many arguments over the question, as everyone has conflicting opinions.
Here, I am going to run down the IDs, from best to worst, with class recommendations (just what's the best, but don't worry, the better IDs aren't bad on other classes, too) and WHY I have picked x over y.
Note: If any drops I list are wrong, or missing (make sure they're useful drops, please...), please correct me.
1. Purplenum
Class Recommendation: FO
FO? This one is simple. Because Purplenum has the best E4 drop chart in the game (Oran comes close). Due to classes such as FOnewm and FOnewearl having such high solo nuking potential, they make perfect solo hunters for the Episode 4 maps. This ID is also very good on a HU/RA, as Purplenum also receives very good drops in Episode 1, too. Unfortunately, not much can be said for Episode 2, but this applies to all IDs, really... (with a few one or two item exceptions).
The Items
2. Redria
Class recommendation: HU
HU? Though there are many other good IDs which may be more 'suited' to a HU (read: Skyly), it's generally better if you give the HU Redria, the RA Skyly and the FO Purplenum, providing you are going to play all three. Redria gets a very good Episode 1 chart, while although the Episode 2 and 4 charts are not as good, they are still decent. Due to HUs having the easiest time in E1, RAs having the easiest time in E2 and FOs having the easiest time in E4, I think you can see where I am going with this.
The Items
3/4. Oran (Tie with Greenill)
Class Recommendation: FO
FO? Arguably, it's Episode 4 drop table easily compares to Purplenum. It might not be as good, but it's still damn good. It's Episode 1 and 2 tables are really lacking, but it's one of the better drop rates of Psycho Wand in Episode 2, along with Purplenum (easily the best due to increase rare enemy rate) and Bluefull. Using techlock spam, it's not too hard to kill the first three Gibbles on PW4, but that quest is done better with a RAmar/l.
The Items
3/4. Greenill (Tie with Oran)
Class Recommendation: RA
RA? Although Greenill is really just a weaker Purplenum, you're honestly better giving Purplenum to the FO, due to the much stronger E4 drop table. Greenill is decent in E4, obtains Guld in E2 and has some decent E1 drops. It's really balanced across all the episodes more so than any other ID, and since RA is the best class in this game (no matter what you think), it's the most balanced option you could choose.
The Items
Anything below this I do not recommend as your starting IDs, but they are decent for specfic items.
5. Whitill
Class recommendation: RA
RA? Simple answer: They're balanced over Episode 1 and 2. Due to the introduction of the Wedding Dress boost, they are one of only three who obtain the armour. Personally, you're better doing Redria, in my opinion, due to it being a trucktonne better of an ID, but Whitill has its items, especially the 1/36 Red Ring drop and Guld.
The Items
6. Skyly
Class recommendation: RA
omfg zyn ur such a noob. Skyly on RA?? LOLWTF!!1 evry1 knows that HU is best ID for Skyly because it gets CS/RS/SJS/Lame!11!!1 and y iz it so low? one of best IDs!! SJS!!!!!11
Okay, please stop. For starters, Skyly is NOT a fantastic ID. The items it obtains are limited, extremely rare or not too great. (CS/RS aren't fantastic, but they're decent). Secondly, please attempt hunting Sealed J-Sword and Lame D'Argent faster than a RA can on a HU. I will bet you that you cannot do it.
To dumb this down, a RA can hunt anything better than a HU can, due to the items they obtain, and the ease it is to play a RA (especially RAmarl/RAcast).
The Items
See what I mean now? Skyly is really not a great ID compared to others.
7. Yellowboze
Class recommendation: HU
HU? It was actually very hard to decide on a decent class for Yellowboze, seeing how it's rather subpar to other IDs... I hear alot of good things about this ID, as it 'apparently' gets alot of good items, but when I put this on my HUcast, I found myself limited to one or two hunts, as the amount of good items yellow gets is rather limited. Due to most of them being in E1, I put the recommendation on a HU.
The Items
7/8. Viridia (Tie with Bluefull)
Class Recommendation: Not HU
Viridia is an extremely bad ID, due to the lack of decent drops it gets. There's a few good items, but it's hard to actually pinpoint anything that's really fantastic about Viridia. I recommend something that's not a HU due to the Limiter drop it gets coming from Girtablulus, and since FOs can Grants Snipe / SoF Demon's, while RAs can Paralyse / Mech Demon's, it's really preferable to be one of those.
The Items
8/9. Bluefull (Tie with Viridia)
Class Recommendation: ...Anything?
Really, really bad ID, in the same boat as Viridia. It gets like 0 decent drops, exceptions being the Punisher for tradebait (or for useless DP / Mille Marteux) and Limiter. Not much I can think to say about this...
The Items
10. Pinkal
Class recommendation: FO, but nothing if you can help it
The WORST ID in this entire game, even with the addition of Shambertin Limiter and Wedding Dress. It gets NO drops, except a minute few, so I do advise to avoid this ID at all costs if you can help it.
The Items
I hope this list helps you decide on a Section ID.
Have fun!