Here we go again...
Best new one would have to include the new TPE livery - best use of non-yellow ends I've seen - looks really modern, dynamic - and seems to work on loco hauled/ 802s/ 185s
Whilst I'm not a big fan of Open Access or of "Adelantes", Grand Central livery does look good on a 180 (i.e. I'm not just picking my favourite trains and favourite TOC here!)
Worst would probably be the new wales AND BORDERS livery applied to the 175 - looks like a really bland "metro" - makes a 100mph train look like a tram - will probably be fine on the Valley Lines - the front of the 175 almost looks like a Class 92 - the old FNW livery really suited 175s because the willow leaf was the right angle to suit the front of the train - now it looks more like it's going to struggle to get to 60mph - not a style suited for long distance stock
Dishonourable mentions to ScotRail and GWR - both very dull
I'm a bit underwhelmed by the "new" Stagecoach EMT livery on the ex-GC HSTs (but then the Stagecoach livery has never been perfect on an HST - it's more suited to DMUs)
Northern livery looks okay on some units, poor on others, but I can appreciate that they have a huge fleet to try to paint and it's hard to find one look that suits everything (since some trains have flat ends, some have curved ends etc - hard to suit both a boxy 153 and a curvy 170
The Inter7City livery looks good if you can ignore the big dark grilles on the side (which I can't!) - one reason I liked the BR HST liveries was that they accommodated the contours of the trains and had the dark "Z" where the big ugly grilles were so that you didn't notice them - the ScotRail livery seems to want to turn it into a feature-piece!
All wholly subjective though - one man's "dull and uninspired" is another man's "crisp and clean" (though I'd echo
@sprinterguy 's point about the blandness of a lot of modern liveries - seems if people can't afford to licence the Virgin brand they just paint their trains sufficiently similar to hope that some of the Branson magic rubs off on them!)