Both Sentry and Raygun are full featured error monitoring platforms. Sentry has better reporting capability, while Raygun has better tools for handling noisy errors. Sentry is less expensive than Raygun. For a cheaper, front-end error tracking alternative that has great reporting and noise management, consider TrackJS.
With TrackJS, the focus is on errors occurring on the browser. Filtering is second to none, and the quick views of trending errors are helpful in digging past the 3rd party script noise. It filters down to the core issues.