Both have different functions, but if I were to pick, than I would say the Reactor is better. Infinity can make all magic Merlin casts to last forever without further draining her mana, but overall the amount of spells that would benefit from that is few, at least when you consider that maybe those kinds of spells already exists and just haven't been used because the amount of Mana needed to cast such powerful spells For example, Merlin uses a Ice spell that freezes the enemy, with Infinity this Ice will last forever, but it can still be broken because it doesn't increase the "power and potency" of the original Ice spell itself, it only makes it so that the spell stays active. If she were to use a more powerful Ice spell, that will use up more mana, because Infinity does not increase her own Mana pool On the other hand, with this Reactor, you can just cast the all-powerful Ice Spell all you want, because you have an INFINITE Mana Pool to use. The Ice spell can be 100000x more potent and powerful than what Merlin can be capable of casting with her Mana pool and it won't be straining with the Reactor providing Infinite Mana

I mean sure you can, the only downside being that it's not instantaneous and will likely take a long time to power it up to that point, and if you try to just dump it all in, which you can't since INFINITE mana, the most likely scenario is that the spell just gonna backfire on you instead In other words, the situation here is that there's the always expanding ocean and then there's you with whatever item, or spell in this scenario, you have, the output is limited and time consuming sure you can fill up the water gun or something like that and have it contain all that water, but isn't it just easier and more simple to just fire off a hydrogen bomb if you're facing off someone that strong in the first place?

it is very literally, infinite mana, although it only means that you have an infinite mana pool to use from, the spells that uses said mana doesn't get stronger than it is already, unless you use something enhances the spell, but even those can only do so much TL;DR: You literally have an infinite mana pool, not spells that do infinity + 1 damage or stuff like that.... unless you actually somehow possess that kind of BS magic

....yeah, "normally"

see this, that's big brain right there

For those that don't know what this is, it is a skill from Tensura series It allows the user to infinitely generate magicules or mana. basically magic energy, thus allowing the user to have infinite mana to use. It also allows the user to use stardust energy, which is the densest form of energy there is, and is also the energy of "everything"

EVERYTHING IS A JOJO REFERENCE!!!!

Now I get it, Middle Two = Chuuni, in other words Chuunibyou Goddess, LMAO