As somebody with both, there are pros and cons to each.

The pros of the pre-installed LED light fixtures is that you wire them in and they work. The cons are, all LEDs fail eventually, and when the ones that have the pre-installed LEDs fail, you have to replace the whole thing unless you are incredibly DIY competent.

A second con of the fixtures with pre-installed LEDs is that some of them, especially the cheaper ones, have issues with buzz. When they are turned on you can frequently hear the transformer humming and to some people that is an annoyance. I am one of those people and I have had to re-replace two entire fixtures because of this.

The pros of the replaceable bulb versions are that since all LED bulbs fail eventually, it is much easier to replace their LEDs. The cons are sometimes the appearance of them aren’t as interesting or fun as the ones with the pre-installed LEDs.

They also have issues with flicker, but that is more dependent upon the bulbs. It has become rather difficult to find a good quality replaceable e27 base bulb that does not flicker or buzz long before the bulb actually fails.

However, since you can replace the bulbs it is easier to make sure that the Kelvin rating of the bulbs matches the rest of the bulbs in the room, and for home use I typically recommend 2700k or 3000k.

Finally, in my personal opinion you should not get any light fixture that uses candelabra bulbs as they seem to have a higher failure rate than the e27s.

Price wise, the pre-installed LEDs can often be cheaper than the ones with the external LED bulbs when you factor in the cost of the LED bulbs.

They both typically have the same ease of installation, which is on par with if you can operate a screwdriver you can install them.

Ultimately it comes down to your competence and self confidence.