Consider the objective or objectives suggested by each pro and con. The pro of one alternative might point to the same objective as the con of another alternative
If there are more than a handful of objectives, arrange the objectives in a hierarchy of homogeneous clusters. For example, you might have a cluster for certain benefits, another for certain costs, another for uncertain benefits (opportunities) and another for uncertain costs (risks). The risks cluster could have long term and short term risks as sub-clusters.
Evaluate the relative importance of the objectives in each cluster of the hierarchy
Evaluate the relative preferences for the alternatives with respect to each of the lowest level objectives in the hierarchy
Synthesize using ratio scale measures to determine the alternative that best meets your objectives
Perform sensitivity analysis and iterate if necessary