That really depends on what campaign you want to model your army on.
Your best choice is Waterloo and Penisular campaigns - as they are only ones featuring Brits in any large numbers and so are most prevailing in wargaming miniatures.
By accident they both feature Wellington although only Waterloo campaign features Napoleon heavily. (Most of the uniforms could be used in both but that depends on your level of purism

(You can play almost all other Napoleonic sub periods but number of plastics decreases dramatically when you are going back in time from 1815 and Wellington is absent).
Uniforms changed a lot in the period.
If you want plastic you have small choice really
Perry
Warlord
Victrix
and to some extent Hat.
From these Perrys are more static, Victrix are multipart (that is pain when you have 60 miniatures in a box..but minis are more interesting if more difficult to paint in bulk)
Best way to se which one you like best is to look for one on one comparison like these.
https://dhcwargamesblog.wordpress.com/2012/07/04/perry-plastic-russian-review/My advice is if you want to play skirmish - Go Victrix multipart.
If you want to play mass battles IMHO Perrys have nicest and sharpest detailed miniatures.
Hat is cheapest but plastic is slightly softer and details could be lacking. I have no deep knowledge of Warlord as I discarded them in favor of Victrix and Perrys as most detailed and didnt bought any.
One thing to mind is that if you want different units in plastic you will have to buy from diffrent manufacturers and combine. Perry And Victrix works well in my experience.