I've ran mine through vroom, carvana and autonation. Vroom sends you an email or two, carvana doesn't contact you at all and autonation did contact me but I informed them I was waiting on my new truck to arrive prior to selling my current 2017. That was about a month ago, got a follow up email today checking on the progress. I don't mind that at all, I really don't like phone calls or constant emails, but I was fine with this type of contact. Autonation also is currently the highest bidder on my truck but I may also try to sell privately if I can sell it quick enough too.
Otherwise autonation will likely get it if they continue to beat the others offers, currently their offer from a month ago was already nearly $5,000 more than my trade in offer from when I ordered in March.
Edit: Worst car buying service thing to use in terms of nagging phone calls, is kbb instant offer. They came in the lowest at the time I tried it and got several phone calls instantly from various dealers.
Same here, I ended up paying around $6-8k more to go brand new factory order, than a 2 year old 10-20k mile truck. And getting the 0% financing (saves $4k over the life of the loan vs my CU rates), it made absolutely no sense to me to buy used at this time.