a sump is easier. I have a 540 gal with a sump, and a 125 with 2 eheim canisters. the 540 is WAY less upkeep than the 125. Here's why...
1. Water changes--On the 125, I have to use a python. on the 540, cause I have a drip system, I don't ever do water changes. drip system changes out half the water a week while I'm sleeping. No sitting in front of the tank while it refills, getting bored and walking off, coming back with a little flood on the floor.
2. cleaning--I have to take canisters out from under the stand, carry them outside, open em up and rinse all the media out WITH tank water. I don't clean the sump at all. I just change the filter socks every 3-4 weeks. that takes 5 minutes or less.
3. size of the sump -- makes it really easy to work. like the drip system. that was really easy to do in teh sump. it'd be very hard in the 125, and i'd have to do it in the display tank--put a standpipe of some sort in there, and the drip outlet in the tank, too. Fish would probably move it one day. or i would while vacuuming.
4. looks better -- in my 540, you don't see a heater. no filter hoses on the back wall. no thermometer. nothing. it's all in the sump. in my 125, i have 2 filter intakes, a big heater, a thermometer, it's all in the tank where you can see it, or you have to hide it with a plant or something.
Yea--a sump is much better.
Is it difficult to maintain? no, it's easier. is it difficult to set up? kinda, but I did it myself the first time off of articles on the internet. if you can glue a stick of PVC pipe into a fitting, you can do it. If you just read some articles about how sumps work, with some drawings, it's not hard to understand at all. You WILL have to think about it, though.