Best bang for your buck would be simple dipoles or something like a G5RV.
Verticals are not so efficient unless you have loads of radials or excellent soil.
This is good advice.
I have a low dipole for 40m, its about 25 ft high.
Even so, it out performs or is on par with my full sized 1/4 wave vertical 95% of the time. Only once have I been able to not hear a station properly on the dipole that I could on the vertical, and that was just because the dipole is closer to the house and more susceptible to noise.
The fact of the matter is for 20M and above, nothing beats a tower and a beam. Not only does a beam give you forward gain, it also gives you QRN/QRM killing nulls on the sides and especially the back.
That said, the fact of the matter is also that with a vertical or a dipole & 100 watts, you will easily get your DXCC in a year if that's your goal. Local communication such as ragchewing will likely be best with a relatively low dipole as well - a beam won't help much here.
For 40M & below, most Hams use phased verticals or dipoles, but this is more out of necessity than choice.
Lastly, don't put too much faith in the whole 'low radiation angle' argument when it comes to a vertical vs a low dipole. Even though the low dipole will have a higher take off angle, it is unlikely that it will be down more than 10dB at useful angles. In other words, it will be within 2dB of a vertical on perfect ground (which none ever are), or about even with a vertical on average ground and 4-8 radials. BUT, it will work a lot better for local contacts... My advice? Enjoy the hobby with what you've got. Play around with cheap home brew antennas such as dipoles, fan dipoles, verticals etc. Find out if you like rag chewing or DXing more. If you like rag chewing most, save for an amplifier. If you like DXing, save for a tower and beam first. With 100 watts and some home brew antennas, you will easily get enough out of the hobby to decide what is next, when the time is right.