Hi and welcome to Coffee Snobs. :)
To get good coffee you need a decent grinder, so if you cant afford that then the Silvia might be a problem as it does need a good grinder to do it justice.... :(
The cheap grinders just dont grind fine enough for the Silvia.
The Sunbeam Id stay away from (they are having too many troubles at the moment)... :-[
The Gaggia is a pretty good machine - but like you - I dont like the Aluminium boiler (dont like Aluminium in food preparing gear plus they corrode rapidly...) :(
So that leaves the Mokita.... A pretty good combo. Has the disadvantage that you cant just upgrade the grinder or coffee machine (well you can but you then only have half the combo)...
Makes pretty darn good coffee by all accounts.... :)
Personally Id go the Silvia and check out the grinders which are a match for it.... That would be the best combo (even if you buy a second hand Silvia- and these are advertised here from time to time)... :)