Depends on many things. Currently and likely to increase rapidly is cost (whether you pay for processing, membership or for publication just to be considered). There is probably a link to the speed of publication for many journals based on one or more of those factors.

In the past (although same circumstances may now not apply) I have found that the common ground journals, linked to conferences they hold, can have quite a quick consideration, review and publication procedure (topic areas are essentially science, social science disciplines, health, education and sport.

http://commongroundpublishing.com/

It is usual to submit a paper for one of their conferences first - if accepted it means you can submit the paper to one of their linked journals. It is possible to obtain acceptance for the linked journal publicatiosn through their consideration and review process prior to the actual conference. Obviously the time lags need to be several months for that to happen but they did have a rule that the conference paper could only be considered for journal publication if submitted prior to three months post conference date,