Here's the most important thing, based on my many decades in the business: Chose the providers in the proper order: First, merchant account provider Secondly, gateway provider. Thirdly, shopping cart provider. If you don't put the cart before the horse, you'll run into fewer compatibility heartaches.

Also, to answer which solutions(s) are best for you:
The answer is: That depends on YOUR unique circumstances such as location, credit, volume, product type etc. The biggest mistake merchants make is being tempted by 'one-size-fits-all" solutions of which there is no such thing.