All three of those Pokemon are effective at dealing with fire/water, taking about 40% on average from a full powered Specs Typhlosion's Eruption with significant Special Defense investment (Mantine takes about that much without any Special Defense investment, so most players prefer to invest in Defense in order to handle a wider variety of threats). Which one you want to use depends mostly on how they work with the rest of your team, as they all have different secondary typings and bring their own kinds of utility to the table.
Lanturn has some good support options, with access to three status inflicting moves and Heal Bell. It can also use Volt Turn off its low speed stat to provide a free switch for a sweeper or work as part of a Volt-Turn core. It's also better equipped to deal with Magmortar than Seismitoad and Mantine are (they're both hit with 4x SE by its coverage moves), but by no means does it counter it. Magmortar falls well short of a guaranteed 2HKO after SR using HP Grass against Lanturn, though it still inflicts a lot of damage. If the Magmortar is running Earthquake, you'll be 2HKO'd after switching into it with rocks up.
Seismitoad is a fantastic hazards lead with an advantage over other common hazard setters in the tier, including Steelix, Camerupt and Archeops. It has decent offensive presence uninvested, access to Knock Off support, and a resistance to Stealth Rock that helps it switch in on Fire moves, though HP Grass coverage is obviously very effective against it. Currently a Special Defense biased Seismitoad is uncommon, but with Kabutops rising and a handful of new answers to Feraligatr dropping, there may be more room for it.
Mantine is the best Defogger in the metagame, particularly notable for countering/checking all current S ranked threats (barring the rare Wild Charge Typhlosion). It also has access to Haze to stop SmashPass, and can function as a soft check to Feraligatr. Unlike Seismitoad, it can switch in on any common Typhlosion move, but you have to be careful, as being worn down by Stealth Rock can put it into KO range.