If you’ve got significant amounts of timber to split then hire in a splitter.
For small amounts I have a fiskars xl27, it’s a weapon but I wouldn’t contemplate using it for more than an hour
Grenades are rubbish. If the fiskars won’t do it a grenade won’t. I have a proper forged wedge that is handy and far superior, they are worth having although you rarely see them. You’ll curse when it’s balls deep and going nowhere though.
If you must split by hand, pick your battles. It’s generally obvious what won’t split so don’t bother doing yourself in over it.
Firewood processing for yourself is a serious pastime. Start now for next winter.
if you must buy in don’t trust anyone to deliver properly dried timber. I see several suppliers locally, none of them store logs in a way that will season well.
In short, hire a splitter