The default house system at Astrodienst is called the Placidus house system, and it is favoured by many because of its sensitivity to timing. Traditional astrologers generally prefer the whole signs house system. The equal house system seems favoured by many British astrologers, possibly because quadrant house systems like Placidus can get very skewed at high latitudes. Many horary astrologers think Regiomontanus houses give the best results.
Your call.
I've always used the placidus system, simply because I think geography must have a bearing on the nature of one's unfolding karma/life. Rudolf Steiner speaks very unequivocally about the specific influences of geographical environment on our souls/psychology/karma etc. I guess maybe I feel that a house being enlarged or diminished is a reflection of the degree of influence of that house, which is reflected in the 'real world' by the fact that a person is born here or there. This leads onto the next point.
I strongly feel that a planet falling into one house or another must be critical and decisive, and profoundly important, so having a 'selection' of house systems seems to be severely at odds with what astrology means to do. Surely we have been working with planets, signs and houses for long enough now to know with absolute certainty that if planets fall in certain houses, they must reflect specific and irrefutable qualities that override any aspects or modifying influences from other planets/bodies/points etc, and as such, should have clarified by now whether or when placidus, equal house or whole sign house systems are applicable or not.
I must say that if astrology is to consider itself a 'science' - which I believe it must do - astrologers really should be finding agreement on which house systems are the most effective, albeit some may be considered to function more effectively for differing purposes e.g. horary vs natal etc, or we'll forever be at odds with each other, and rightfully be branded a pseudo-science or a superstition by outside observers.
The fact that astrologers 'know' astrology is a working and reliable system is of no consequence to those who would venture in from outside, and be put off by the seemingly illogical applications of random rules and systems. Not that that should matter per se, just as physicists have no responsibility to placate artists for example, however there is a certain responsibility on our parts to be clear for astrology's sake.
I have no idea which system applies with absolute certainty, so I can only venture an opinion, like most of us here, and for me Placidus has served me well enough. A lifetime of experience will hopefully inform a rounded view in each of our cases, and perhaps those experiences will some day lead to a settled house system we can all agree upon.