My Maltese is very picky and is hard to please with food. I give him no table scraps and am feeding him natural balance as of now.
You have a couple of options. The one I would no personally choose, is to buy several brands of dog foods and put a little of each out a short distance apart. See which one he likes. This is a slippery road, though. My Grandmother used to keep multiple bags of dog food in the house and if the dog didn't immediately choke down her food, she said she didn't like that one anymore and switched her. That kind of thing costs a lot of money and leads to stomach trouble for the dog, though. Animals prefer a consistent diet. I'm not saying that they wouldn't prefer an occasional addition to their food, and most will always go after people food, but as far as their health and digestive system, they prefer a steady diet. It's why I don't feed mine anything but dog food and training treats. I think it's good that you're not feeding people food.
What I did personally is research and look up what the top quality foods are. I found a list somewhere, I can't remember where at this time, but an independent group had evaluate multiple pet foods and come up with an extensive list of excellent dog foods. Sufficed to say, but I didn't even recognize the names of the top 10. These people automatically disqualified any brand that had grains or meals added. Just whole meats and veggies. They also disqualified a lot because of recalls. They included subsidiary brands that tried to pretend they weren't part of the larger company that had a lot of recalls. I think "Taste of the Wild" fell into that category.
I actually found one of the brands on that top 100 list at a local store. I switched my dog to that and she seemed to like it pretty well. I blended the last of her old food with an increasing amount of her new food to switch her over without upsetting her stomach.
In the end, though, I don't pay much attention to what she wanted. While I'd like her to like her food, there really isn't as much option as you'd think. All you can do is look at the best pet food and get the highest level that you're willing to put he time/money into. Ideally, the best pet food is prepared people grade food, such as boiled or grilled chicken, fish, lean meats, steamed vegetables, etc... The problem there is you don't know if you're giving them all the nutrients and necessaries that they need to be healthy. You could prepare every mill by hand out of high quality ingredients and still make your pet sick or unhealthy because you're depriving them of something by not adding it to their diet. It's also time consuming, expensive, and labor intensive.
The next step down is to buy the raw foods, then down from that are the canned wet foods, and dry food is below that. I prefer dry food, because of ease of storage and usage. I buy the highest quality I can reasonably afford.
Whether you get something trashy, like Old Roy or prepare mills by hand, you're basically getting the best you can, so that really limits your options to 3-4 or less in your level of food. Of course you can then pick up a small bag of each of these and let your dog choose, if you want.
Other than that, I don't really believe that are dogs that are picky eaters. I know I'll probably get a down voter or comments on it, but I believe its almost exclusively projected on pets by owners. As an example to support my theory, I'll use my grandmother's dog. She was extremely snobbish about food. Even steak had to be cut up, cooled to the proper temperature, and left out for her convenience. She was stolen once and managed to get loose from the people, based on a later eye-witness account. She was loose for ~1 week. I burned through several tanks of gas searching for her. Turns out, the man that saw her escape from the thieves car fed her for a couple of days, then she was on her own for the rest of the week. When we got her back, for about a month afterwards, she'd eat anything you put down for her. Then my grandmother started babying her and switching her food around and she went back to her old ways.
We later inherited the dog. When we first got her, I'd put pieces of boiled chicken or some other healthy treat out for them. She'd turn her nose up and walk off. One of the other two immediately inhaled it. She came back 15min later and was looking for it to eat it. She pretty quickly learned to eat when she had the chance. She became much less picky from that point on. She got plenty to eat, but knew she needed to eat what she was given then and there or wait till next feeding. Between consistent diet and more exercise, she actually became much healthier.
So if it were me, I'd put the dogs food down for 15min twice a day. If she's still actively eating after 15min, let her continue, but if you put it down and she doesn't eat for 15min, then take it up and let her wait. Repeat at the end of the day. It won't take but a couple of days and she'll start eating. It may seem a little cruel, but it's actually healthier. You can control quantity, unlike with free feeding, and you also help regulate when they have to go to the bathroom and help prevent accidents in the house. Good luck and I hope you find a good dog food.