yeah ehiems are the best but by far the most expensive. and i believe 125 litres is about 32 gallons which in my opinion is not worth the money for any canister filter, I personally would recomend a hob filter for anything under 55 gallons, if you want to spend the money go ahead get the ehiem but Myself would use a aquaclear atleast the 200 model or higher you can buy two ac 500's or 110 for the price of the cheapest ehiem and one ac 500 is rated for 150 gallons, quite simply the better buy
fyi, internal filters are sponge, undergravel, box, and powerhead types such as fluval plus or ehiem aquaball, while external filters are more than jsut canisters but HOBs, trickles, fluidized bed,...