I have four seats for three bikes.
My K75S has a Corbin, recovered by Sargent. It is brutally uncomfortable for rides longer than an hour, but seems to be softening up a tiny bit after about 8,000 miles. On the other hand, it's a really nice looking seat and makes the bike look really nice.
My K75RT has a Russell Day Long seat. I chase horizons with that bike and that seat is good for 12-14 hour long days in the saddle. It's huge and probably wouldn't look good on a sportier ride.
My K100 RS has a BMW Comfort seat. It is at least as comfortable as the Russell, but not as large. I use that bike for commuting and day rides, the seat is perfect for that. There are a fair number of them available on eBay for prices between $100 and $200+. IMO it is a good choice between comfort and sportiness.
I also have the stock "plank" that came with my K100RS. I have it for when I sell any of my bikes so I can keep the seat I have on them right now.