Tory Zac Goldsmith pledged to deliver a Southern Overground and secure funds for Tramlink, Bakerloo Line and London Overground extensions.
Labour's Sadiq Khan said he would freeze fares and crack down on what he called a "culture of excess".
Rival candidates want to cut fares but said Conservative plans were "uncosted".
Unveiling his manifesto in Ilford, east London, Mr Goldsmith said he would deliver planned upgrades to the District, Circle, Metropolitan, Hammersmith & City, Northern and Jubilee lines, and would replace "sub-standard" suburban rail services with a Southern Overground.
He also spoke of securing funding for Crossrail 2 and extensions to the Sutton Tramlink, Bakerloo Line and London Overground to Barking Riverside, saying that delaying or cancelling these projects would risk 250,000 jobs and 270,000 homes.
He said: "And it's why Sadiq Khan's Â£1.9bn black hole in the transport budget would be such a dangerous experiment, bringing gridlock to our capital, fewer new homes and meaning council tax hikes for every family in Greater London."
Outlining his transport pledges in Brixton, south London, Mr Khan recalled riding on the number 44 bus with his siblings, when his father drove the bus.
"I'll be the bus driver's son who makes commuting more affordable", he said, adding: "I will wage war on waste, excess and inefficiency within TfL and crack down on the culture of excess."
He also promised a four-year fare freeze, a review of Transport for London (TfL) management, projects which "truly benefit Londoners" and more women on TfL's board. He said he would look at the amount spent on agency workers and consultants, currently said to be Â£383m a year.
Lib Dem mayoral candidate Caroline Pidgeon said Mr Goldsmith's manifesto was "an uncosted wish list".
"He makes no mention of any fare rises, and he appears to be relying on government to keep on funding London's transport network."
Green Party candidate Sian Berry has promised to lower costs for outer London, introduce flat fares by 2025, allow transfer between buses and trains without an extra cost and support walking and cycling.

One hundred tracks by artists including Ben Howard, Kendrick Lamar and SBTRKT have been shortlisted with voting open until 9pm on 27 November.
Lana Del Rey, You Me At Six and Eminem also feature on the list.
Zane will count down from 100 to one between 1 to 4 December.
The 1975, whose track Chocolate topped the poll in 2013, also appear in this year's list with their track Medicine.
Why'd You Only Call Me When You're High? by Arctic Monkeys and Shadow Moses by Bring Me the Horizon completed the top three last year.
Ed Sheeran's Sing and Stay With Me by Sam Smith, which both went to number one in the UK, also appear on this year's shortlist.
Gecko (Overdrive) by Oliver Heldens and Becky Hill and Clean Bandit's Rather Be, which also topped the chart, feature in this year's top 100 too.
Mercury Prize nominees Bombay Bicycle Club, FKA Twigs, Royal Blood, Jungle and Nick Mulvey all appear as well.
Voting for the 100 Hottest Records is limited to one per person, full terms and conditions can be found on the Radio 1 website.
Follow @BBCNewsbeat on Twitter and Radio1Newsbeat on YouTube
Conservative and Labour mayoral candidates have set out their transport manifestos, with a "war on waste" and Tube and train expansions promised.
[NEXT_CONCEPT]
Throughout 2014 Zane Lowe has picked his hottest records in the world, and now it's time for you to pick your favourite.