I have become a fan of fermenting the seeds the last few years.
Cut the tomato in half and squeeze seeds into a glass jar, plastic container, something and add a little water. I take a piece of plastic ( have been cutting off bread wrappers) secure on top with a rubber band and poke some holes in the plastic. Give it a shake on day 2 and by day 3 or so you will see the viable seeds have sunk to the bottom of the container and a scum has formed on top of the liquid. I just pour the scum off and fill the jar with water then. The seeds will settle to the bottom again in just a few seconds and I pour off the bits of tomato in the water and non viable seeds that remain. Repeat once or twice more and pour off most of the water just using my fingers to keep from pouring the seeds out as well. Shake the seeds out onto drying tray and forget about them for about 2 weeks. ETA: On day 2 after you put them on a drying tray, break them seeds up and spread them out good. It's much easier to spread them out after the excess water has dried up. THEN forget about them for a few weeks.
Super easy and nice clean seeds. But if I am saving seeds from only one tomato I will still just put them on a napkin or a paper plate or something. I don't know if there is one best way as much as it is what works for you and how many seeds you are trying to collect at one time.
I ferment mine too, similar to bid's method. But I dump mine in a mesh strainer and rinse under water, then dump on a plate and dry. I like how clean they come out. I can tell a lot of the non-viable ones because they'll be dark or off-colored and I pick those out while wet.
Also be sure you pick a very ripe off the vine, mature tomato for the best developed seeds. Choose tomatoes that were the best/healthiest among your plants and exhibited desirable qualities.
I love fermenting my own tomato seeds and enjoy saving tomato seeds and growing our own tomatoes at home from them. Home-saved tomato seeds are a wonderful gift to tuck into a holiday card for when you want to add a "little something extra", or to share with friends and neighbors.