Hmm, I too (as an adopted Southendian for the last few years) am not crazy about the town. Being so close to London makes it a bit more cultured than it would otherwise be, believe it or not! It's definitely smarter than it once was (the less said about some of the new university buildings despoiling the town skyscape the better), but there's a lot that could be done to improve the place, if some imagination was to be found. But, yes, anywhere - anywhere, without exception, well, except for Whitstable - on the north-facing side of Kent is far, far worse! (in pat I blame this on the quality of light resulting from the sea being to the north) Margate (and especially Cliftonville)is just dire, and when I last visited Herne Bay struck me as being overly well provided with tattoo and piercing parlours for such a small place! Great Yarmouth is dire in the extreme. Canvey is not exactly pleasant - but kind of interesting in a slightly horrific manner.
Loved St Andrews when I was a student there, but calling that a "seaside resort" (even though it is), seems to understate it somewhat! Some of the other villages on the opposite coast of Fife (which I suppose are mostly rather upmarket seaside resorts), especially Crail and Elie/Earlsferry are lovely, too, St Monans and Pittenweem pleasant enough, Anstruther (Easter) rather less so. And the whole Leven-Buckhaven-Methil conurbation is worth avoiding, as is Tayport. (But maybe here we are stretching from "seaside resort" to "coastal town", which is not quiet the same thing) Portobello (although it's really part of Edinburgh) is alright.
And in Essex...given that we have one of the longest coastlines in the country Clacton is vile, Jaywick worse (although kind of interesting for its uniqueness. Where else can you find muddy, unpaved streets named after brands of cars, filled with strange shacks that started out as summer houses, and really should have stayed that way). Frinton pleasant if excessively respectable, Walton-on-the-Naze has some charm, once you get to the Naze itself particularly.
Harwich is a curious and somewhat incoherent place, still a working port, with a rather characterful old town, a perpetually run-down area around the main shopping street (near Dovercourt station), and a fine beach-and-cliffs-setup along the south coast of the estuary.
Burnham-on-Crouch has a lot of appealing things about it, but, as far as I know, no decent restaurant for many miles around.
Brightlingsea is the place that the last few decades forgot (still, maybe that is fewer decades than some of those places I mentioned in Fife), but none the worse for it. Very slow-moving, isolated and mostly agreeable, I think.
Maldon - 2nd nicest town in Essex I reckon (after Saffron Walden). Characterful and filled with good things. Pity there are no trains!
A small selection from elsewhere in the UK...
Brighton is in spirit as much a city as a seaside resort, with all the pros and cons that it brings, Bognor Regis....is to my mind unremarkable, Sandown and Shanklin both...about the landscape (and palm trees when they were still a novelty in the UK), but not very much more.
Haven't been to Blackpool or Hastings for over 20 years, so they may have changed a great deal in the meantime, so I won't comment.
Nuclear power station places too small and remote to really qualify as resorts: Dungeness and Bradwell-juxta-Mare- both rather fascinating, peculiar, wonderful, scenic bits of remoteness, with the steam railway in one and the 6th century chapel in the other adding to the interests
And (token Welsh seaside resort I've been to) Cric(c)ieth seemed alright enough, I suppose. if a bit insecure about how many "c"s it has in its name.
Folkestone's harbour area and town centre isnt too bad, although it's main seafront area could do with being made better somewhat. Ramsgate, in my opinion, just has a fair bit of charm to it, especially along the front itself (although I accept that, again, there are some areas I wouldn't want to live - thankfully I live at the nicer end of town!)