I presume you live in the UK, so it would make sense to buy the coin of the nation you live and work in. This aids in its recognition but also that fact that those coins may have tax and sales benefits. Brits are CGT free. The Royal Mint states:
There is however a VAT premium that comes with the purchase but I believe there is a petition with parliament to have this ended. In the meantime VAT still stands.
If you want silver purely for value, then it would be advisable to buy as many troy ounces as you can for the £5k. Counting in ounces would be the goal and so this might mean picking up a stash of buy-back silver, bars, or more niche products. It ultimately doesn't matter as silver buyers will recognise each product.
I would also think as an investment it would be wise to hold on to this for a while, maybe 5 years or more. The long term trend of silver is a gentle upward slope but there is a lot of volitility in the short and medium term. If you are able to stomach those peaks and dips then do get a stack.
I first purchased silver in mid 2016 and so saw a steady decline in its currency price over a three-year period. Being able to wait it out and seen the currency price rise was a relief to a new investor.