In 10 years i expect the world will be a very different place. At some point precious metals, especially silver will come into their own.
You don't give an amount you are willing and able to spend.
Let's assume silver increases in price with inflation and let's assume inflation is 5% or less per year. The reason i say that is, if we see hyperinflation the price of silver could go up to £1000's per ounce, that is assuming the GBP survived. There may be new uses for silver and silver suddenly becomes more vital and scarce. In such circumstance getting as much silver as possible will have been the best policy. Silver could become so valuable the actual coin becomes irrelevant.
However let's assume things potter along as they have up to now.
A coin has two value elements. The value of the silver and the value of the coin. Coins with the same silver content have different prices and this is due to the value of the coin, the collector [numismatic] value.
I would look closely at the selling side of this forum. You will find some very good value coins appear here. i have bought lots of coins here. What comes up is a bit random but you are about spotting good value coins with potential. From your question it seems to be you are looking to have a stack of maximum value in 10 years time. In that case i would not restrict myself.
Certainly Pandas have been a good buy in the past. You usually get best value in recent years before the numismatic value of the coin increases. The problem with Pandas is their mintage numbers aren't known exactly but the potential mintages are very large. Having said that there are enough Chinese to swallow the mintages many times over. So if you were buying a coin from a dealer, getting Pandas would be a good choice but getting single coins is generally uneconomic when it comes to dealer postage charges. Buying silver from UK dealers is also lumbered with VAT which makes it more expensive - another reason to buy off this forum. This forum is generally better value and much surer than ebay.
If you are collecting a small number of coins i would not bother with basic bullion coins - Philharmonics, American Silver Eagles. I would not get anything Canadian b/c of milk spot. i have had problems with milk spot with Somalian Elephants. I believe Armenian Noah's Ark coins have above average trouble with milk spot.
From the view of tax - although it does not seem this would be an issue with 12 coins per year, buying UK coins exempts you from Capital Gains Tax.
Buy coins you like the look of.
Don't buy gimmicky and generally coloured coins.
Get proof coins with COA's if you can find good value coins.
Get coins in a series even if you don't intend to get the whole series.
Get coins with lower mintage that collectors might want if they are completing a series - you might get 2oz or 1/2oz coins which are produced in much smaller numbers than the 1oz.
Do some research by looking at how prices vary over time and between mintages - https://www.gold.de/kaufen/silbermuenzen/
This is in German but it is not hard to follow and you can look at how different weights, mintages and mints vary.
Perth Mint publishes mintage numbers
There is more to it than this but it is a start.