Hi bud.
I was happy with NAPIT to be honest. Their customer service absolutely trounces NICEIC as they are keen to keep you happy and their website works! The NICEIC website is broken and won't allow you to make online payments towards your fee's etc. Also, their online shop is broken too! Can't order any logo's for the van, t-shirts....anything really. I've put in a support ticket but have had no reply from over 3 weeks ago so they certainly take their time getting back to you!!
I attempted to use their online certification software too but there doesn't seem to be a guide on how to efficiently use it (no problems in filling it in, just how to do it quickly) so I abandoned that and went back to my trusty EasyCert software that I've been happily using for some years now.
As far as the assessment are concerned, the NAPIT assessor was certainly a LOT more relaxed than the NICEIC guy. Was with the NAPIT guy for half a day but a full day with the NICEIC.
NICEIC guy was a lot more in depth as far as paperwork and compliance was concerned and wanted to see more variation with site work too. He was quite specific with what he wanted to see as far as Inspection & Testing was concerned too.
If you decide to go with NICEIC, be prepared to be waiting around for them to get the wheels in motion but, this will give you more time to prepare really. If you want to go on the Private Rented Scheme for landlord assessments, this is now a separate thing and no longer an "opt in" so you'll need your paperwork AGAIN for that.
Also, TrustMark, if you intend to go with those, that is also a separate thing and no longer "opt in" so it's paperwork AGAIN.
If you call NAPIT to change to NICEIC, just tell them you're going PAYE (don't say you're joining NICEIC) for a while and they'll offer to store your details on file for £99 which will mean you can basically jump back into NAPIT without having to go through all the registration process all over again!
Might be worth considering if things don't go to plan with NICEIC.
Ultimately, NAPIT is the easier choice as they're much more customer focused and the assessments appear to be a bit more relaxed.
I only went with NICEIC as it was a requirement for a large contract I wanted to tender for. I'll stay with NICEIC now for the forseeable future.
Oh, and be prepared to pay double-----initial assessment fee of around £600 then, if you pass, you'll then pay a joining fee of around a similar amount. It ain't cheap bud!!!