Your town or airport. We'll compare flying, driving and transit to Colorado Springs from there — driving wins when it should.
Getting in
Colorado Springs Airport: Uber/Lyft or a pre-booked taxi/car service is the sensible move: roughly 20–30 minutes to downtown, longer to Manitou or north Springs, with variable surge pricing. Mountain Metro Route 37 connects the airport to Hancock Plaza, but requires another connection for downtown; at $1.75 or $4 for a day pass it is cheap, but slow and annoying with luggage.
Denver International Airport: For convenience, book Groome Transportation's scheduled shuttle to Colorado Springs; allow about 90 minutes at best, and more with I-25 traffic and multiple Springs stops. The cheaper option is RTD A Line to Denver Union Station (about 37 minutes), then Bustang South to the Colorado Springs Downtown Terminal; realistically budget 2½–3½ hours door to door, plus a transfer and another ride for Manitou or Garden of the Gods.
Colorado Springs intercity rail: There is no operating intercity passenger-rail service or station. Use Bustang for the Denver connection; do not plan around proposed Front Range rail.