The best tank for a planted aquarium is one with a big "depth" - front to back dimension. A 29 gallon or 55 gallon tank is too "shallow" - too little front to back room - to allow many options for a good looking aquascape. A 75 gallon tank is the same size as a 55 gallon tank, but with almost 50% more front to back room, so it is vastly superior for a planted tank.
I think the best size for a tank is the biggest one you have room for, money to set up, and time to maintain. It is unusual to hear someone complain about their tank being too big, but many people complain about it being too small.
If this will be your first planted tank, I suggest you consider it to be a learning tank, where you can learn to be comfortable with fertilizing, with CO2 injection, with pruning techniques, etc. For that, a 29 gallon tank is about the smallest I would try. (I'm prejudiced, because I used one for that purpose, when I realized I really knew nothing about planted tanks.) Smaller tanks are harder to judge light intensity in, are less stable, and have too little room for plants.
My current tank, still a learner tank, as far as I am concerned, is a Jebo tank I bought on Craigslist - about 45 gallons, and with a great shape for planting, but a small footprint so it takes little room in my condo.