theme parks

does anyone have an opinion about these 3 theme parks? - universal studios, disneyland and disneysea.

my partner & i (aged 30 :)) would like to visit them but would only like to choose 2 as we think we will get overdosed on themeparks after visiting all 3!

does anyone also have tips on buying these park tickets? ie. how to avoid queues, buy beforehand, etc.

Which theme parks to chose depends on your personal preference. Universal Studios feels a little bit smaller than each of the Disney parks.

As for avoiding crowds, try to avoid school holidays, national holidays and weekends. Go on regular weekdays when kids are in school. Then it is not necessary to buy tickets beforehand, but you can just buy them at the entrance.

School holidays are second half of March and early April, from mid July through August and the last week of December and early January. National holidays are listed on the following page:
http://www.japan-guide.com/e/e2062.html

my choice would be disneyland and sea. you can save on their 2 day pass (a day for each park). and it could save you money and time on the shinkansen (4 hour max) or train (could take 12 hours or more) going from tokyo to osaka (USJ).

In terms of interest for adults, I think Universal Studio and Disneysea would be your best bets.