The best sharpener is the one you have on you. So I'd start with the Mobius and Ruppert Brass Bullet Sharpener that offers a keyring to attach to your keys.
https://www.amazon.com/Mobius-Ruppert-sharpener-KEYHOLE-0604-90/dp/B072Q8HDQT
After that, just buy a box of these Apsara Long Point sharpeners. Toss one of these bad boys in every drawer and bag and you'll be golden.