Silver has the bigger upside potential but it's also more volatile, less sure. Can't go wrong with Gold long term. There's a move, I'm not sure if there's a technical term for it, I just call it the gold silver flip flop. Right now buy silver at the 114:1 ratio, when it gets down to something like 40:1, trade in for 3 ounces of gold. then if it returned to 80:1, you trade back and now have 240 ounces by only paying for 114. Historically (long ago) ratio was in the teens or twenties. More recently 40 is low and 80:1 is starting to get high. >100 i wouldn't touch gold.
You can add to your position by buying the one that's favorable at the time you want to purchase.
Right now there's a COVID-19 panic. Dealers were blitzed for bullion and there's a back order because business was otherwise slow. Premiums are crazy, sometimes as high as 100% for silver ounces (meaning you pay double spot price). What I don't know is how much longer before the next run up. It was $50 USD/ounce in 2011 before being artificially smashed down by future contracts on the COMEX (I call it the CRIMEX). If you find at $25 USD now, it might seem steep, but it's half of the previous high. It's really up to you to decide what's right for you.
Also in general, yes you'll pay less premium for bars but the coins are the best option in my books. Don't forget, you'll get part of that premium back when selling.
