I find many of the German Bicolors/yellow/orange varieties good. Kellog's Breakfast, Pineapple, Paw Paw, never tried a bad one! Many are also old and endangered varieties from our area, Seedcorn. Garden Peach is another good one that fits into the category.
I haven't tried many of the black varieties, Black Trifele is a great one it has a hard-to-describe kind of chocalate undertone flavor. It has a nice pear shape and dark black color inside, attractive tomato overall.
I've tried a few cherry tomatoes and they never fail to produce a good harvest.
I've been on an oxheart kick lately, mostly the orange or yellow types. Obtained this unidentified orange oxheart from a close neighbor, will post pictures and distribute seeds when I grow it out. (It needs a name, there are too many orange oxheart varieties out there to tell what the heck this is!)
Other than that I really don't have a "favorite" tomato. I'd say just look around and find something that sounds interesting to you. The Sandhill Preservation Center is a great place to start as they have a huge selection of cheaply priced tomato varieties to choose from.