Honestly, as a total lover of both this is an apples and oranges comparison.
I am going going to only consider what I consider "real" between these two brands, that's ESP (MIJ) and Ibanez Prestige and above.
ESP is a true custom shop
.They'll build whatever you want, if you have the cash and the time to wait.Their custom shop is among the best if not the best in the world. The ESP standard series are awesome guitars. Tons of different options and choices, even though better if you live in Japan than the USA. ESP also offers a first rate luthier school and you have a high chance of working for them when you graduate.
All said, there is no other "big brand" that offers what ESP does.
Ibanez is a brand based upon in house design and OEM production. They cannot offer anywhere near the range of customization as ESP. They are production guitars, built to the highest standard. Great value for the money and IMHO the Wizard II/Wizard Prestige is the best neck ever. The RG is a classic and their in house design of hardware is first rate (Edge/Edge Pro/Tight End.)
Really though for me it's bang for the buck. I can buy a used RG550 and mod the hell out of it so I end up with a custom guitar and still come in less expensive than an ESP M1 standard. Not really fair,but true.Ibanez also builds the best case in the biz with the Prestige case.Seriously, a 10K ESP doesn't come with a case half as good.
That being said, if money is no object it's all about ESP. I prefer the Wizard II but could ESP copy it exactly? You bet. You get what you pay for in a custom guitar and ESP is the best option for this. Why? I could have just as much customization from "Joe's Customs" but the resale on ESP's is awesome. Even an M1 Standard from 1998 still is hard to find for under $800.00. On resale,ESP beats Ibanez too.
At the end of the day I love my RG's, if money were no object however I would have custom ESP's and never look back.