The harrowing thing about the first two is that both are matters of opinion, and worse yet, usually someone else's opinion. Since violin dealers seem to make a sport of disagreeing with one another, the musician looking for an instrument can be left in a miserable nervous quandary. One of the biggest differences between looking for an antique instrument and a modern one is that both is that authenticity and condition are both givens in the latter case. The nervousness and resentment that can grow out of the necessity of relying on other people's sometimes fickle opinions is gone. This certainly matches the excitement of owning an instrument that has had many experiences you have not shared.
Sound quality is still the major factor in choosing an instrument, new or old.
So a little preparation is necessary in order to learn what sound you like best. Before you spend time and money going around looking for instruments, play every instrument you can get your hands on, borrowing them from friends, teachers, and stand partners. Play every instrument at length-for hours, not just minutes. Instruments vary in material and build, and each will make subtle, or even drastic, demands on your technique before you get the best sound. Chances are great that the technique you use on your present instrument won't be an instant success on others.