Survivor Gabon and Tocantins (Seasons 17 and 18) are my personal favorites, and are the first two seasons in HD. I find that watching Survivor seasons in order isn't necessary, and watching some of the later seasons then watching Season 1 later is really interesting / entertaining since you're able to see how much the game, and the way it's played has evolved over time.
Big Brother seasons are all pretty consistent I find. 6 and 8 in particular was pretty good if I recall correctly. However, I recommend you don't start on 9 since it follows a different format, 7 since it's an All Stars season (Definitely worth watching though), and it's not a group of strangers like the other seasons, or 13 since it features returning house guests.
tl;dr:
Survivor: Gabon and Tocantins
Big Brother: 6 and 8
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XBL / PSN: lol im ahkmed