Notepad
I'm not kidding. No automated sheet out there will perfectly reflect your house rules or campaign. They'll also contain information you don't need, or be missing fields you do need. Multiclassing is rarely supported well.
I've even tried making my own character sheets in MS Word or Excel, and I end up having to modify them every time to really capture a character "just right". It's easier and cleaner to stick with a text file. Plus text files have the advantage of being cross-platform to everything, so you can [work on your character from/share it with a DM using] a home PC, iOS device, etc. in addition to your main tablet.
Every character I make has two text files. The first one is the "audit trail" where I list out their race, background, and which level they've reached in each class they have, and what they picked at what level. So I can see that at 4th level I put an ASI into Wisdom, for instance. This file is only used when leveling up or when my DM asks me where X or Y feature came from.
The second text file (or Word file with a simple grid of text boxes) has static modifiers (stats, AC, HP, etc.) listed at the top, and then all the actions I can do sorted by action type (standard, bonus, reaction, move, etc.). This is a lot more condensed and useful during play as I can quickly scan what my options are in a given round.
