I've a Yamaha DTXpress III kit.
Good to start on, but I'm thinking of moving to Roland's TD-12, or if I have a moment of madness, possibly a TD-20.
I'm frustrated with the Yammy kit, sounds great, but it soon becomes clear your playing a 'triggered' kit, cymbal crashes especially. It can sound 'drum machine like'.
Roland's higher end kits vary the sounds depending on how they are played, and as a result they sound much closer to a real kit.
Yamaha will always win when price is the deciding factor, but for me, Roland's 'attention to detail' has one me over.
Not sure about the Yamaha DTXpress IV either, it lacks a MIDI input, which is a massive step backwards to the previous models.
Roland's TD-9 might be worth checking out, heard some good reports about them.

There is always the older TD-8 and TD-10's these where Roland's higher end kits not so long ago.

Saw a Alesis set-up at a show recently, the words 'cheap & nasty' came to mind.

It's worth a look at both Roland's and Yamaha's sites, watch a few on-line demos to give you an idea of what they can do, and the features they have.

A second hand Yamaha DTXpress I/II/III would be my 'starter' kit if I where starting over.
My set-up has been taken as far as it will go. After hearing, and see what a Roland kit can do, it made me look at mine in a whole new light. Then started thinking, "what if.."

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