Noise and privacy tend to worry first-timers more than they need to. Units are generally spaced with a reasonable gap between them, and most parks are quieter in the evenings than people expect, particularly outside peak school holiday weeks.
Coast and countryside both make for a good UK break, so the real question is what kind of days you want to have rather than which is objectively better.
Day trips are where staycation budgets often quietly slip, so it's worth planning a mix rather than assuming every day needs an admission ticket. A coastal walk, a free stretch of beach, or a wander round a market town costs nothing beyond fuel, and mixing these in with the odd paid attraction keeps the week varied without every day carrying a ticket price.
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Next, think about park size. A larger park usually means more on-site facilities: a pool, a clubhouse, perhaps a shop and a play area, which suits families who want options if the weather turns. A smaller park tends to be quieter, with fewer people about and a slower pace, which some guests prefer, particularly couples or those travelling without children. Neither is better, they just suit different trips.
Day to day, you'll be doing your own cooking and washing up, much as you would in a self-catering cottage, so it helps to bring a few kitchen basics like tea towels and washing-up liquid rather than assuming everything will be there. Bedding is usually provided, but it's worth checking your specific booking, since this varies park to park.