I'd say it's broader than which children, as both LAs and VAs have adopters who have adopted all kinds of children.
It varies between LAs and VAs. Talk to a few. Ask about ongoing support, not just what they're legally obliged to give, but support through to adulthood and beyond.
VAs can be more accepting of adopters who are single, or gay, or have medical problems.
You can do FtA/concurrency via a VA.
"Harder to place" is a difficult phrase, and I wouldn't get too hung up on it.
LAs may have their own children to place, but if you get to the end of the process, and none of their children are your children, then that can be difficult. It's a matching process, you don't want to be pushed to be matched with a child because it's the one the LA has, and you're the one approved family, for instance.
For one family, in one area, a VA may be everything they need. In other families, in other areas, the LA may be superb. Talk to what's around you, read the OFSTEDs, and see who gives you a good vibe.
There are many threads on LA vs VA, and powerful advocates of both.