I love fireline great sighting, good feel and i have had no issues with knot tying to leaders or mono.
What was the problem with the fireline you used?

I have used a number of different braids. 1 in particular has been great however i can't remember what it is maybe GORILLA braid.

I also usen playtapus and fire line and have tried spider wire when it first came out.

Platypus super-braid 30lb is my choice

G'day
Not being knit picky but fireline isn't really braid it's known as thermally fused. However i found that it seems to break when it bcomes twisted after use when lure casting etc. I would say that Fins braid is my favoured i have it loaded on my bait caster and spinning rod. Also have used platypus super braid with no complaints.

When it comes to knot problems i found that Fins is very good with joining knots with mono. I use the albright knot which works well. On the light spinning gear my brother tells me to use a double and then tie a (cairns quicky) or a simmilar albright not. He uses a bimmini twist (i can't do that yet) so i use the spider hitch for my double. If the albright does slip that could mean not enough twists when tying the knot, or if this is not the case i have seen super glue used in a small amount on the knot.

Cheers
ACE