As a complete Topps set builder of all base/traded sets from 1951-present, I don't concern myself with variations/errors too much. I tend to get the card that easiest to get, or typical for the set. Here are some examples:
*In modern Topps sets, I collect the factory set rookie variations.
*In the late '80 there were variations where some cards had a trademark, and some didn't. Are you kidding me? Never noticed.
*In 1988, Al Leiter had an incorrect picture card. I made sure to get the correct picture. I don't care about the error.
*In 1977 or 1979, there was a variation that looked like someone had drawn a circle with a magic marker. I made sure to get the one without the magic marker look
*In 1979, Bump Wills had an error card that labeled him as a Blue Jay. He didn't play for the Jays, but the Rangers. I got the Rangers card.
*In 1969, there were 2 cards that had variations of a player with two different teams that they played for. I consider these Traded cards and collect these.
*In 1962, there were a whole bunch of cards that were considered green tinted. I don't even pay attention to this variation
*In the late '50s/early '60s the card backs had either white stock or grey stock. Although I prefer grey stock, I take what I can get
*In 1951, there were also 2 cards that had variations of a player with two different teams that they played for. I also considered these Traded cards and collect both.
Basically, there are what I consider "stupid" errors/variations, and "legitimate" errors/variations. I stay away from stupid errors, or very expensive versions of error. I don't know (nor do I want to know) someone that's willing to pay $700 for a 1990 Topps Frank Thomas RC error with no name on the front. That's silly.