Running the Minn Kota 55lb on a 4m tinnie, I pilot and love it.
Check the amps usage and you may go with the Minn Kota.
How many volts 24, 36 ?

I run the new 80lb 24v XI5 Gps Motorguide on my Sea Hunt centre console 18'6,  works like a charm, spot lock really locks you down unlike the minn kota which tends to drag around the wind abit if it's up, the down side to that is a bit more consumption on the batterys. I got mine through CHsmith in Vic, they might be worth an email for more info.
No problems with it in two years after moderate use so i can't comment on after sales/warranty, but like all leccys, it's more than likely going east for repairs like i've had previously with watersnakes and minn kotas with serious issues, some minor repair's or replacements can be handle by the local agent, but not always.

Have a chat with MickC from ShoreCatch (Site sponsor) as he is into the benefits of the trolling motors and can supply them as well. 

 Thanks for the info guys . Battery life is not an issue as it wont get used for long periods . Its just to hold the boat in an area while casting poppers . And the 36v with 3 x 120ah batteries should be heaps i think . Just wanted to hear of any issues with claims as im in karratha

 I was keen on a moror guide for the lowrance interface but no suppliers here. Youtube motorguide lowrance hds. Can use the sounder to auto pilot back to a spot i.e. fish school and spot lick it. Minn kota only interface with hummingbird