We are using a RESTlet over SOAP, personally, even when the REST API comes out of Beta completely, we will still use the restlet as we have done things like use native python arguments in the query of the reslet and translated that to work within NetSuite. We have also tailored some of the behaviours in our restlet to do some funky stuff all in one request, rather than needing to fire off multiple such as:

create_invoice

then repeatedly

transform_to_payment

if we provide a list of payment objects on the invoice, whilst with the rest api you will be doing 1 request to create the invoice and then one for each payment, which if you are creating multiple invoices with multiple payments in a single request, will reduce the number of requests to the API