Newquay is best avoided in the summer, unless you are a student. It's a bit too lively (full of drunks).
Perranporth is too close to Newquay, and has a huge holiday camp.
Ilfracombe is very run down, and is a real pain to get to.
If you want a quiet family holiday, you can't beat The Lizard. Excellent beaches at Ruan Minor/Kuggar (Kennack Sands), and several smaller beaches either side. Small fishing villages (Coverack, Cadgwith), and some spectacular cove beaches (Kynance Cove).
Further towards Penzance, the beach at Porthleven (Loe Beach/Loe Bar), and Praa Sands are good, and Mount's Bay is worth a visit.
The north coast is where all the rabble go, the south coast is for families.