With 435 House seats up for re-election only 40 are in any meaningful risk of changing parties. This is in part because of redistricting, the periodic reconfiguring of political boundaries to enhance the control of the party in power.
While I am in favor of a less partisan redistricting process this may not make as much difference to the outcome of elections than a few other election reforms, among which my favorite is the Blanket Primary. My aim is shared with the original framers of the constitution who wanted the House elections to be a referendum by the public on the direction of the government. Any favoritism to incumbents defeats that objective.
Blanket Primary - The top two vote-getters from each office advance to the general election, regardless of party affiliation. This means that the general election could be between a moderate Republican and a conservative Republican.
Open Primary - Voters need not publicly declare their party affiliation but must vote for candidates of only one party. The opposite is a closed primary, in which only registered members of a party may vote.
Instant Runoff Voting - single winner elections in which voters rank candidates in order of preference. In an IRV election, if no candidate receives an overall majority of first preferences the candidates with fewest votes are eliminated one by one, and their votes transferred according to their second and third preferences (and so on), until one candidate achieves a majority.
Condorcet - this system measures which candidate has the broadest support. It compares each candidate pair-wise with each other candidate.
Borda Count - this is similar to how college football teams are ranked. A first place vote is worth 4 points, a 2nd is worth 3 points, a 3rd 2 points and a 4th is worth 1 point. The candidate receiving the most points wins.
Approval Voting - each voter votes for as many candidates as they like. The candidate with the most votes (plurality) wins. Approval voting only measures whether a candidate is acceptable to the voter; it does not distinguish between a candidate who is intensely liked and those who are more weakly approved of.
Cumulative Voting - this system was used in Illinois for 110 years until 1982 to elect Illinois House of Representatives. Voters had three votes to give to three candidates and could distribute the votes any way they wished - all to one candidate, one each, or two and one. There is a push now to revive it. See the Drive to Revive Cumulative Voting.
Voters should select their representatives rather than elected officials selecting thier voters.