Ok, here goes
The two choices are relatively similar although the shorter focal length and therefore wider field is probably a better option as it will provide a better comprimise between land and astro viewing. The 70mm F/13 with 90mm objective??. If that is correct it is most probably because the optics are poor in quality (poorer than the scope should have). To get around poor optics one method is to stop down the aperture (90mm to 70mm) to get rid of the worst of the aberations such as vignetting, usually by inserting a field stop inside the tube. The multiplication figures such as 675 times are something of a misnomer. An economy scope combined with atmospherics mean that the liklyhood of getting to that number is small and the viewing even if you could would be marginal at best. I have $13000.00 worth of F/11 scope and last weekend I could not get past 559x and even then the image was a mess. The number makes great advertising but its usefulness is limited to nil.
In my opinion a better alternative for your money would be to buy a decent pair of binoculars giving at least 80mm to each eye or better. I have attached a link to Andrews Communications
http://www.andrewscom.com.au/site-co...section-11.htm
where you will see a range of binoculars including 100mm aperture with zoom eyepieces. do your numbers and you should be able to get a tripod to go with it. A little further research and you can build your own
Parallelogram mount that enables easy deep sky observing. It is often overlooked but some very fine astro observing can be had with binoculars of 80mm or more. It probably isn't what you wanted to hear but the 70mm refractors on ALT/AZ mounts are really limited in what they can be used for astronomically. a combination of a long tube with narrow FOV means that objects are hard to center and even harder to keep there (assuming you can find them with a 5x24 finderscope). The flexure of the mount and tripod makes this problem even worse. I saw one of these scopes arrive at a dark sky night in Melbourne a couple of years ago and the owner couldn't center Saturn in the eyepiece. A couple of us went over to help and we couldn't do it either because as soon as you had it in the FOV and let go of everything the flexure moved it away.
OK, it probably sounds like aperture arrogance and I certainly don't intend it to but I have been where you are (my first was a 4" Tasco 11TR from Myers and I loved that scope to death) and would see you get the best for your money.
Recapping, first suggestion is Binoculars for that amount of money, second is that you go with a wide field short focal length refractor on an ALT/AZ mount.
Good luck and good hunting.
Paul Medcraft