The answer is different for both series. The Bioshock games are best played in order as their stories link in with one another, so you're best playing Bioshock 1 first. With Fallout, you have more options, as most are their own self-contained story and setting. Personally, unless you're looking to dive deep into the series, I'd avoid the first two titles (Fallout 1 and 2) as their controls and gameplay mechanics might be a little too outdated to handle at first. A perfect first option, in my opinion, is the latest title in the series: Fallout 4. It will appeal most to the modern gamer and is the easiest to jump into.