It’s Cech for me. While Leno might be more used to passing the ball out from the back, the German is an inferior shop stopper to Cech, is prone to making more errors and crucially, is less dominate at claiming crosses.
That last facet of goalkeeping is particularly significant in the Premier League, and it is a key reason why Ospina, who struggles in that department despite being a superior shot stopper to Cech, has been unable to usurp the former Chelsea stalwart.
Personally, I think Arsenal made a costly (£19 million) mistake in recruiting Leno, given they already have two impressive younger goalkeepers on their books in Martinez and Macey.
That said, it doesn’t appear the club has done, nor is it intending to do, their contracted goalkeepers any favours, but recruiting a coach in Emery who is notorious for employing a high defensive line and recruiting and/or retaining relatively slow and immobile central defenders in Sokratis, Mustafi, Holding, and an aging Koscielny.
As previous Premier League seasons have shown, a goalkeeper’s effectiveness is very much linked to the effectiveness of the defensive scheme and defensive personnel that protect them. For Arsenal’s current cohort, it appear that the lack of protection they experienced under Wenger will continue under Emery.