Nearly all avionics companies shop each other for price which means the best avionics companies may be only a few dollars higher than the marginal ones.
Buy avionics from a company specializing in avionics and that is able to provide technical assistance and will support their products after the sale.
The FAA must sign off on any radio installed in an aircraft. Always deal with well known companies when purchasing a radio and get a full warranty in case it needs to be returned.