If you go down the NEST route then its is probably simper and cheaper to administer. The LGPS route is very expensive for a parish with some hidden stings in the tail. Each County has a different scheme so you will need to research very carefully the costs involved. It can take several months to sign up to the LGPS scheme as they have to do an assessment in each case, before letting you in. One problem to be aware of is that if, say, the Clerk resigns, and is not replaced by another one on the LGPS, then there may be a cost to pay for contributions lost to the scheme, in order to fund the resigned clerks entitlements in the future.
Take lots of advice and if going the NEST type pension route ensure you get a supplier that has good accounting procedures and doesn't mess up the contributions required, or just use NEST of course.