I don't know if you are restricted to land-based dive operations or not, but I'll try to offer some help in either case.
I've been to PNG 4 times, once diving Milne Bay aboard Chertan, and 3 times aboard Febrina, which is based at the Walindi resort. On three of the four trips, I stayed and dove at Loloata at the beginning of the trip, before flying on to the ultimate dive destination.
Loloata is a real gem, largely undiscovered except by experienced dive travelers. It is hard to believe that there could be world class diving within a half hour of Port Moresby, but Loloata really has it - wrecks, pygmy seahorses, sea snakes, colorful reefs - tons of photo opportunities. I HIGHLY recommend that you spend at least 3-4 days there, regardless of wherever else you're headed. Each time I've been there, I've thought that if I hadn't travelled halfway around the world to get somewhere else, I could spend an entire dive vacation at Loloata. Dive there at the beginning of your trip, just in case you need to wait for delayed baggage to arrive. The only negative I can think of is that Loloata often has a nearly unbearable combination of heat/humidity. Be SURE to get a room with air conditioning; you'll thank me I promise, and will consider the small extra cost well worthwhile.
I can't discuss Tufi, but I know a bit about Walindi. It is located on Kimbe Bay, and dives some of the best dive sites in PNG (and indeed the world). If you can, I suggest that you try to spend part or all of your time there aboard Febrina, which is able to get a bit farther afield than Walindi's day boats. But if not, you'll find the diving in Kimbe Bay delightful. It hasn't been voted the best land-based dive resort in the world in the past for nothing. I'll attach a photo of a Rhinopeas scorpionfish, and another from one of Febrina's favorite dive sites, Krackafat Reef, which has huge schools of jacks and barracuda.
In short, I don't think you'll be unhappy with Loloata and/or Walindi.
As for routing, from the U.S. you'll likely be flying via Aukland/Brisbane or Sydney/Cairns. I'm not aware of any cheaper/simpler routing.
HTH,

