SwiftKey — Bought by Microsoft. Pros: Has long-press for symbols. Reasonably configurable. Dedicated number row. Has long-press for diacritics. Long-press on the spacebar to move the cursor. I like the way it treats emojis -- not intrusive, but still there when I need it. Cons: Almost no cons.
GBoard — By Google. Pros: Has long-press for symbols. Nice configurable options. Dedicated number row. Can move cursor by swiping across spacebar (though I couldn't personally get this to work). Cons: No long-press for diacritics.
Smart Keyboard — Pros Has long-press for symbols. Can move the cursor with either the volume buttons, or by swiping. Dedicated number row (but this doesn't add any more symbols -- frustrating!). Con: No long-press for diacritics.
AnySoftKeyboard — Pros: Probably the most configurable items of any keyboard. Cons: Doesn't have long-press for symbols.