Consider what your reaction would be to a presuppositionalist who asked you if you could be wrong about everything you know. I've already written what I would say to this question in a post a while back that it's impossible for me to be wrong about everything I know. Some things I know for sure logically. But, the question now arises, what kind of knowledge am I most certain about? So here's a few considerations.
1. Logical truths about abstract objects and math. It seems to me that logical, or a priori truths about abstract objects would rank highest on the list of things I am most certain about. I know, for instance, that the three angles of a triangle add up to 180 degrees. And even if the external world around me were somehow all an illusion, this would still have to be logically true.
2. Empirical truths about the external world. Scientific empiricism is the most reliable way to discover truth about the external, physical world and as such, when it comes to ontology, this is the preferred epistemology. The successful track record of science and empiricism is further evidence of this.
3. Observational truth about the external world. They say seeing is believing but that is not always so. We use non-scientific observation all the time in our daily lives as the means by which we know things to be true and it is often reliable. However, we do not always see things as they are and sometimes our minds can trick us. Memories can also be influenced and confabulated especially when we're under duress.
4. Logical truths about the external world. We sometimes infer what exists in the external world using the processes of deduction, induction and abduction. Although they are often reliable, pure logical reasoning alone is not always the best epistemology when inferring truths about physical reality. No logician for example, would ever be able to come up with the rules of quantum mechanics sitting in his armchair. Empirical evidence is needed to know many of the truths of the external world.
5. Intuition and faith based truths. Human intuition and faith based epistemologies are the most unreliable because they neither seek logic, reason or empirical evidence to discover anything about the external world. These epistemologies are what religions often rely on: using emotional to guide one towards truth. Arguably, something taken on faith that hasn't been logically or empirically verified cannot be said to be truth, and the failed track record of faith as an epistemology is proof positive of this.
Some might say that logical truths about abstract objects first involve input from empirical truths about the external world. I'm sympathetic to this argument. We learn about math as kids by using physical objects as representations of numbers before we learn that the numbers can operate abstractly. But I'm working here under the scenario in which the validity of our senses comes under question. In that case, it would seem to me that logical truths about abstract objects would offer the most reliable certainty since the negation of their truths would be impossible. But this doesn't allow the introduction of the concept of god as being a logical truth any more than it does ghosts, demons or leprechauns. The ontological argument to prove god's existence using pure logic fails on many levels, and we have good reasons to think the classical concept of god is illogical.