Chunnel

Its your money. You decide. Look here: http://www.seat61.com/London-to-Paris-by-train.htm#Eurostar_classes_explained

Well, as we are currently going thru the Chunnel at this moment (isn't wifi great) when we got in and sat down I said to hubby...I should have priced out first class...lol. But it isn't too bad...more legroom than an airplane...

We thought the standard seating was just fine, especially with a table to spread out our lunch and champagne as we sped toward Paris. It's a short trip, and standard is WAY better than airline seating.

1st class won't get you there any faster. And I hear they no longer allow goats and crates of chickens in standard anymore, so you're probably safe there.

It's only two hours and a bit after all and heavenly compared to 130 minutes in Economy class on a plane these days. And you won't get bumped.

I will say when we walked by the first class compartments on the way out, those seats looked heavenly. But I'm too cheap :(

The 'mid-tier' offering on Eurostar has been progressively downgraded in content, although the differential against standard price has not changed - widened if anything.

First class tickets entitle you to a half-bottle of wine and a small lunch. For the money spent, it's not worth it.
Second class is fine - the trip is only 2h22 - and you can bring your own food and beverages on board, including alcohol.

Tip: "Chunnel" is somewhat disdained in Europe. They are more inclined to call it the channel tunnel. The real price concern lies in buying tickets far in advance which could provide enough savings for a decent meal in Paris. Meanwhile, pick up a sandwich or whatever in the M&S food shop St-Pancras. You'll barely have time to digest it.