As if you're not confused enough already...
There is another type of boiler not yet considered. A system boiler. Would be best of both worlds. Is used with an unvented cylinder which is mains fed not tank fed. This is regarded as the best system in terms of performance. No tanks in the loft, mains-pressure hot water, cylinder with immersion backup. Plus modern, fast-recovery cylinders heat up very quickly. Unvented cylinders need an annual inspection, but it's a must with boiler these days otherwise you won't get the full warranty so just get them checked at same time.
To be honest, I'm sure any system will be fine (combi, heat only or system). All have their advantages and disadvantages. In terms of cleaning out loft tanks, if you do keep your current system, get a lid so that cleaning isn't needed.