Only a tough decision because there aren't really any wrong answers
Our summer holidays in childhood always used to be on the pastel green section, around about the middle of the coastal section. This has the bright lights of Newquay with it's different beaches including a surfing beach, but can get a little boisterous. However there are some lovely beaches that are probably still not badly spoiled by tourism. St Agnes was the regular beach, nothing special in the beach but a lovely moderately steep road down that made it quite picturesque. Frozen mars bars were the big treat, but for us kids the parrot called Solly who people had trained to swear was an obviously puerile joy
. Portreath had a lovely feel to it, and Porthowan was a nice wide open beach with natural salt water dipping pool from when the tide went out. Chapelporth had the appeal of nothing being there, so you got a feel for how the area was before tourists appeared. The coastal walking is excellent, but sampling the beaches is also recommended.
Looe in the darker orange section is a quaint fishing town, nice feel to it.
Truro in the pastel purple section is the county town, but I recall it being nothing of any real substance - an administrative centre rather than a destination.
Lizard point (lime green) and Lands End (darker blue) have geographical appeal as most southerly point and one (with John O'Groats) of the two furthest extremities of the mainland. Whilst you might not see the same excitement in such geographical positioning, the landscape is nicely rugged here, but not somewhere I'd jump at to base myself.
Padstow (Pastel green / bright blue border) is jokingly referred to as Ric Stein-ville after the TV chef who owns a few restaurants there. He's made it more popular, but also made this an option as a place to eat out well. Just north of there is Tintagel castle, a significant landmark.
A lot will depend on what you're looking for, but I'd be tempted to base on the coast (NW or SE) as this is a very fine coast, so finding a place with a good view of a scenic coastline should be good for the soul.
I hope this helps and apologies that my experience is now a little dated, things may have changed a lot since I last visited in the early 1990s!