I have just bought a Boardman CX team bike for my commute to work and to generally potter about on. It feels OK but the tyres are a bit of a shock coming from a road bike. I think they are some pretty cheap and basic nobbly Schwalbe tyres, 35mm. My commute is a mere 3.5m on mainly road and cycle paths, so I want something a little faster and more suitable. But, I also want something comfortable and reliable. My favourite choice so far (based on a small amount of research and reviews) are the Schwalbe marathon (or Plus). But, not sure on size, 35, 32 or 28mm. I do want something a little more suitable to the pot holed roads and cycle paths with the option of the odd trail. So I am thinking maybe 32mm, or will I still find them sluggish on the road? Any suggestions welcome, I can look at other tyres too if they are recommended.
You don't say what's wrong the current tyres nor have you expressed what you want from alternative tyres other than comfort and reliability. Comfort is a matter of tyre pressure and you can many any tyre comfortable or uncomfortable with a bicycle pump. That's leaves reliability. That's vague and I can only guess you mean puncture protection. All good brand name tyres are reliable.
Here's some guidelines to decide if you have the right tyre for the job.
1) If the tyre cannot leave an imprint on the surface of the road, they should be slick, not knobbly.
2) If the tyre can leave an imprint on the road (i.e. soft stuff you're riding on), then a tread pattern is useful.
3) Slick tyres have less rolling resistance than an equivalent treaded tyre.
4) Given the same tyre casing and tyre pressure, a wider tyre has less rolling resistance than a narrow one.
5) Grip is not dependent on width unless you are riding in mud, where narrower offers more traction than wide.
6) Puncture protection comes from more rubber on the tread. This also brings with it higher rolling resistance. All heavily puncture protected tyres are sluggish by comparison to their thinner-skinned cousins.
7) Tyre width relates to tyre volume. The wider, the more volume you have and volume is inversely proportional to pinch flats typical of potholes. Thus, the wider the tyre, the less chance of a pinch flat, provided you maintain sensible pressures.
My suggestion is to ride your existing tyres until they are bald. They will improve in all aspects as they wear down. I.e, they will not deteriorate, but improve. Adjust your tyre pressure for the required comfort.