I'm currently using Chemical Guys New Look Trim Gel which is good, leaves a nice finish (can be glossy or matte) and lasts well when applied to a properly cleaned tyre.
Only down side is there can be a little sling if you apply too much or dont buff it enough.
I've got my eye on Zaino Z-16 at the moment... looks very good.
The Meguiars endurance gel smells like raspberry ice poles too. Nice little bonus.
So many to choose from in my opinion.
Two that i really like the now
Autosmart highstyle Blackfires Long Lasting tires Gel.