Proton aside, Soyuz is singly the most reliable launch vehicle on the market, since the retirement of the US Shuttle and ULA Delta II. It has both the longest track record of anything out there, if you look at the entire R7 family, of over 3500 flights. It also has a success rate of over 98% over the past thirty years. The Delta II reached a similar ratio, but over only 140 flights. Also, the Soyuz is one of only three vehicles that Arianspace is able to launch from French Guiana.
Edit: I should probably note, Delta II isn't completely retired yet. So the two are sorta kinda still tied. I've been a Delta II fan for a while, but they're down to selling off stockpiled hardware. Prices kinda went through the roof with the GPS contract going to EELVs. It's a shame, since it's the end of a fairly good track record. But we still have Soyuz.
Oops... Edit 2, since I can't edit this anymore. R7 has not flown over 3500 flights in 60 years, it's flown ~1600 flights. 749 on the model retired in 2011. http://astronautix.com/lvs/soya511u.htm
Edit: I should probably note, Delta II isn't completely retired yet. So the two are sorta kinda still tied. I've been a Delta II fan for a while, but they're down to selling off stockpiled hardware. Prices kinda went through the roof with the GPS contract going to EELVs. It's a shame, since it's the end of a fairly good track record. But we still have Soyuz.