I had two trainers simultaneously when I first started. One was a tail dragger, the other a trike.

Can't say I noticed too much of a difference.

For me the biggest factor was flying from less-than-perfect grass, where the dragger would sometimes nose over. Cost me a prop or two.

I'm an old-fashioned sort though and don't think there's any subsitute for experience. Regardless of the end goal, I'd suggest getting experience of every type and configuration of model you possibly can. You can only learn.

The trike will probably save a few props and a few walks to collect.

In honesty I couldn't keep either plane in a straight line as wheel alignment of models flying off grass isn't quite the science it is one real aircraft........

If it were me being asked for an honest opinion, I'd say go for a trike first to get used to operating a model, then get learning tail dragging.

The old Precedent T-180 was and still is the best 2nd model I've ever flown. My father built our one on a friend's recommendation and it teaches a student how to fly PROPERLY. It needs rudder in the turns, swings on take off and needs to be flown to a halt on landing. That said, it's very easy to fly safely, it just flies ugly unless you make the effort to tidy your flying up. It's possibly slightly fragile for use as a first model (read "lawn dart"). By that I mean it wont tolerate the common very early mistakes such as wrong control inputs in banks etc. It can be stalled on landing without show-stopping damage though.

Anyway, I digress. I'd recommend a trike for the very first model, and a decent sized tail dragger for the second.