So, i know everyone says bishop better at everything and all, but it looks painfully unfunny to level and i just prefer to level a fun class, i can leech a bishop with it later. What class is more fun and better at leeching, ice/lightning or fire/poison?
F/P is easier to level with poison mist, you can grind at high level mobs at low level and get insane exp. Both are equivalent at giving leech, only difference is blizzard freezes mobs.
From my experience F/P mages are cheaper and easier to level than I/L mages. Assuming you're aiming for petri leech (end game leech for both classes) a notable difference between the two is the price of wands. Both classes need to have 1257 magic to one hit petri (1260 if under 1,000 int), but Elemental wand 7 comes with a disadvantage, it's secondary stat is LUK instead of INT - so it has lower base magic on average and few places drop it (only CBD and LHC iirc). This contributes to a large price gab between equal TMA wands. Other than that, I/L blizzard quest can be time consuming as you need a rare drop from a mob. F/P mages can speed through lower levels without leech by using poison breath (2nd job) and poison mist (3rd job) to tag high level mobs and cc (example to get the idea). There are benefits to playing I/L mages in more niche content like LHC/NT/TOT/Ellin farming as they can freeze mobs that they can't one hit which is a big deal. If you are strictly only interested in the leech aspect, I think F/P mages are superior. If you want to keep the door open for future content or being able to explore more niche farming spots, I/L mage would be better