Half the fun is trying the strains that you have had good reviews on from several people saying the same thing. Start with the GorillaGlue and Stardawg and PurpleStardawg, or the ones mentioned for PopeofDope. Before spending three times the amount of money on Runtz (which I believe is a 'cali' strain, correct me someone if I am wrong, not tried it) I have tried cali stuff tho, which for me personally is a rip off if you are in the UK, and you run the risk of fake cali tins. I was not impressed with the cali, besides I was on the hunt for a strain that I could get easily and regularly for normal prices.
You will have to invest a bit of time and money trying the strains mentioned in this topic, but its worth it to find the best strains for yourself/dad. To be honest after many many buys when I first joined, I thought I would never find my strain, and then I tried the stardawg, which I bought a little of one time to try. Back then tho I didn't realise that I needed to switch to an indica dominant, so I was buying up all that loopy sativa. :)